Repository: apna-college/Cpp-DSAClasses
Branch: main
Commit: df2f65cb2bfa
Files: 26
Total size: 55.1 KB

Directory structure:
gitextract_eps2mzau/

├── .gitignore
├── 04_Conditional_Statements/
│   └── conditionals.cpp
├── 05_Loops/
│   ├── homework.cpp
│   └── loops.cpp
├── 06_Patterns/
│   └── patterns.cpp
├── 07_Functions/
│   └── functions.cpp
├── 08_Binary_Numbers/
│   └── binary.cpp
├── 09_Pointers/
│   └── pointers.cpp
├── 10_Array_1/
│   └── arrays.cpp
├── 11_Arrays_2/
│   └── arrays2.cpp
├── 12_Basic_Sorting_Algos/
│   └── sorting.cpp
├── 13_2DArray/
│   └── 2DArrays.cpp
├── 14_String/
│   └── strings.cpp
├── 15_Vector/
│   └── vectors.cpp
├── 16_Bit_Manipulation/
│   └── bit_manip.cpp
├── 17_OOPS1/
│   └── oops1.cpp
├── 18_OOPS2/
│   └── oops2.cpp
├── 19_Recursion1/
│   └── recursion1.cpp
├── 20_Recursion2/
│   └── rec2.cpp
├── 21_Divide_and_Conquer/
│   └── divideAndConquer.cpp
├── 24_Backtracking/
│   └── backtracking.cpp
├── 25_LinkedList1/
│   └── ll1.cpp
├── 26_LinkedList2/
│   ├── doubly_linkedlist.cpp
│   ├── linkedlist.cpp
│   └── list_using_stl.cpp
└── README.md

================================================
FILE CONTENTS
================================================

================================================
FILE: .gitignore
================================================
.DS_Store


================================================
FILE: 04_Conditional_Statements/conditionals.cpp
================================================
#include <iostream>
#include <cmath>
using namespace std;

int main() {
    //Print the largest of 2 numbers
    int a = 3, b = 5;
    if(a >= b) {
        cout << "a is larger" << endl;
    } else {
        cout << "b is larger" << endl;
    }

    //Print if a number is Odd or Even
    int num = 5;
    if(num % 2 == 0) {
        cout << "Number is Even" << endl;
    } else {
        cout << "Number is Odd" << endl;
    }

    //Income Tax Calculator
    int income = 7; //in Lakhs
    float tax;

    if(income < 5) {
        tax = 0;
    } else if(income <= 10) {
        tax = 0.2 * income;
    } else {
        tax = 0.3 * income;
    }

    cout << "Tax = " << (tax * 100000) << endl;

    //Print Largest of 3 Numbers
    int x = 2, y = 3, z = 5;
    if(x >= y && x >= z) {
        cout << "x is largest" << endl;
    }   else if(y >= z) {
        cout << "y is largest" << endl;
    } else {
        cout << "z is largest" << endl;
    }

    //Odd or Even using Ternary Operator
    int num = 25;
    bool isEven = num % 2 == 0 ? true : false;
    
    //Calculator using Switch Statement
    int op = '*';
    int num1 = 4;
    int num2 = 5;

    switch(op) {
        case '+' : cout << "a + b = " << (num1 + num2) << endl;
                    break;
        case '-' : cout << "a - b = " << (num1 - num2) << endl;
                    break;
        case '*' : cout << "a * b = " << (num1 * num2) << endl;
                    break;
        case '/' : cout << "a / b = " << (num1 / num2) << endl;
                    break;
        default : cout << "Invalid Operator" << endl;
    }
    return 0;
}

================================================
FILE: 05_Loops/homework.cpp
================================================
#include <iostream>
using namespace std;

int main() {
    //Qs : Factorial of a number n
    int n = 6;
    int fact = 1;
    for(int i=1; i<=n; i++) {
        fact *= i;
    }

    cout << "factorial of " << n << " = " << fact << "\n";
    
    //Qs : Multiplication Table of n
    n = 8;
    for(int i=1; i<=10; i++) {
        cout << (n * i) << " ";
    }
    cout << endl;

    //Qs : Check for Armstrong Number
    n = 371;
    int num = n;
    int cubeSum = 0;

    while(num > 0) {
        int lastDig = num % 10;
        cubeSum += lastDig * lastDig * lastDig;
        num /= 10;
    }

    if(n == cubeSum) {
        cout << "Armstrong number\n";
    } else {
        cout << "NOT an Armstrong number\n";
    }

    //Qs : Print Primes from 2 to N
    int N = 15;
    for(int i=2; i<=N; i++) {
        int curr = i; //current number to check for
        bool isPrime = true;
        for(int j=2; j*j<=i; j++) {
            if(curr % j == 0) {
                isPrime = false;
            }
        }

        if(isPrime) {
            cout << curr << " ";
        }
    }
    cout << endl;

    //Qs : Print N Fibonacci Numbers
    n = 10;
    int first = 0, sec = 1;
    cout << first << " " << sec << " ";

    for(int i=2; i<n; i++) {
        int third = first + sec;
        cout << third << " ";
        first = sec;
        sec = third;
    }

    cout << "\n";
    return 0;    
}




================================================
FILE: 05_Loops/loops.cpp
================================================
#include <iostream>
#include <cmath>
using namespace std;

int main() {
    int n = 10;
    //Print numbers from 1 to n
    // for(int i=1; i<=n; i++) {
    //     cout << i << " ";
    // }
    // cout << endl;

    //Print numbers from n to 1 (reverse order)
    // for(int i=n; i>0; i--) {
    //     cout << i << " ";
    // }
    // cout << endl;

    //Print Sum of first N natural numbers
    // int sum = 0;
    // for(int i=1; i<=n; i++) {
    //     sum += i;
    // }

    // cout << "Sum from 1 to n = " << sum << endl;

    //Square Pattern using For Loop
    // for(int i=1; i<=4; i++) {
    //     cout << "****" << endl;
    // }

    //Sum of Digits of a Number
    // int digitSum = 0;
    // int num = 12345;

    // while(num > 0) {
    //     digitSum += num % 10;
    //     num /= 10;
    // }

    // cout << "sum of digits = " << digitSum << endl;

    //Sum of Odd Digits of a Number
    // int oddDigSum = 0;
    // int num = 12345;
    // while(num > 0) {
    //     int lastDig = num % 10;
    //     if(lastDig % 2 != 0) {
    //         oddDigSum += lastDig;
    //     }
    //     num /= 10;
    // }

    // cout << "sum of odd digits = " << oddDigSum << endl;

    //Print a number's Digits in Reverse
    // int num = 12345;
    //
    // while(num > 0) {
    //     cout << num % 10 << " ";
    //     num /= 10;
    // }
    // cout << endl;

    //Reverse the given number & print the result
    // int num = 12345;
    // int res = 0;

    // while(num > 0) {
    //     int lastDig = num % 10;
    //     res = res * 10 + lastDig;
    //     num /= 10;
    // }
    // cout << res << endl;

    //Check if a number is Prime or not
    int num = 49;
    bool isPrime = true;

    //Solution 1
    for(int i=2; i<num-1; i++) {
        if(num % i == 0) {
            isPrime = false;
            break;
        }
    }
    cout << isPrime << endl;

    //Solution 2 (slightly better) : #include <cmath>
    isPrime = true;
    for(int i=2; i<=sqrt(num); i++) {
        if(num % i == 0) {
            isPrime = false;
            break;
        }
    }
    cout << isPrime << endl;
    return 0;
}

================================================
FILE: 06_Patterns/patterns.cpp
================================================
#include <iostream>
using namespace std;

int main() {
    int n = 4;

    //Number Square Pattern
    for(int i=1; i<=n; i++) {
        for(int j=1; j<=n; j++) {
            cout << i;
        }
        cout << endl;
    }

   // Star Pattern
    for(int i=1; i<=n; i++) {
        for(int j=1; j<=i; j++) {
            cout << "*";
        }
        cout << endl;
    }

    //Inverted Star Pattern
    for(int i=1; i<=n; i++) {
        for(int j=1; j<=n-i+1; j++) {
            cout << "*";
        }
        cout << endl;
    }

   // Half Pyramid Pattern
    for(int i=1; i<=n; i++) {
        for(int j=1; j<=i; j++) {
            cout << j;
        }
        cout << endl;
    }

   // Character Pyramid Pattern
    char ch = 'A';
    for(int i=1; i<=n; i++) {
        for(int j=1; j<=i; j++) {
            cout << ch++;
        }
        cout << endl;
    }

    //Hollow Rectangle Pattern
    for(int i=1; i<=n; i++) {
        cout << "*";
        for(int j=1; j<=n-1; j++) {
            if(i == 1 || i == n) {
                cout << "*";
            } else {
                cout << " ";
            }
        }
        cout<< "*" << endl;
    }

    //Inverted & Rotated Half Pyramid
    for(int i=1; i<=n; i++) {
        //spaces
        for(int j=1; j<=n-i; j++) {
            cout << " ";
        }
        //stars
        for(int j=1; j<=i; j++) {
            cout << "*";
        }
        cout << endl;
    }

    //Floyd's Triange Pattern
    int num = 1;
    for(int i=1; i<=5; i++) {
        for(int j=1; j<=i; j++) {
            cout << num++ << " ";
        }
        cout << endl;
    }

    //Diamond Pattern
    for(int i=1; i<=n; i++) {
        for(int j=1; j<=n-i; j++) {
            cout << " ";
        }
        for(int j=1; j<=2*i-1; j++) {
            cout << "*";
        }
        cout << endl;
    }

    for(int i=n; i>0; i--) {
        for(int j=1; j<=n-i; j++) {
            cout << " ";
        }

        for(int j=1; j<=2*i-1; j++) {
            cout << "*";
        }
        cout << endl;
    }

    //Butterfly Pattern
    for(int i=1; i<=n; i++) {
        for(int j=1; j<=i; j++) {
            cout << "*";
        }
        for(int j=1; j<=2*(n-i); j++) {
            cout << " ";
        }
        for(int j=1; j<=i; j++) {
            cout << "*";
        }
        cout << endl;
    }
    
    for(int i=n; i>0; i--) {
        for(int j=1; j<=i; j++) {
            cout << "*";
        }
        for(int j=1; j<=2*(n-i); j++) {
            cout << " ";
        }
        for(int j=1; j<=i; j++) {
            cout << "*";
        }
        cout << endl;
    }

    
    return 0;
}

================================================
FILE: 07_Functions/functions.cpp
================================================
#include <iostream>
using namespace std;

//Simple Function
void sayHello() {
    cout << "Hello from Apna College\n";
}

//Sum of 2 numbers
int sum(int a, int b) {
    return a + b;
}

//Sum of 2 float - Function Overloading
float sum(float x, float y) {
    return x + y;
}

//Product of 2 numbers
int prod(int a, int b) {
    return a + b;
}

//Is Number Odd or Even
void evenOrOdd(int n) {
    if(n % 2 == 0) {
        cout << "Even\n";
    } else {
        cout << "Odd\n";
    }
}

//Factorial of n
int factorial(int n) {
    int fact = 1;
    for(int i=2; i<=n; i++) {
        fact = fact * i;
    }

    return fact;
}

//Prime or Not
bool isPrime(int n) {
    if(n == 0 || n == 1) {
        return false;
    }

    for (int i = 2; i*i <= n; i++) {
        if(n % i == 0) {
            return false;
        }
    }
    
    return true;
}

//Binomial Coefficient nCr
int binCoeff(int n, int r) {
    return factorial(n) / (factorial(n-r) * factorial(r));
}

//All primes in range [2, n]
void allPrimes(int n) {
    for(int i=2; i<=n; i++) {
        if(isPrime(i)) {
            cout << i << " ";
        }
    }

    cout << endl;
}

int main() {
    sayHello();
    cout << sum(1, 2) << endl;
    cout << sum(1.0f, 2.0f) << endl;
    cout << prod(1, 2) << endl;
    evenOrOdd(25);
    cout << factorial(5) << endl;
    cout << isPrime(5) << endl;
    cout << binCoeff(4, 2) << endl;
    allPrimes(15);

    return 0;
}



================================================
FILE: 08_Binary_Numbers/binary.cpp
================================================
#include <iostream>
using namespace std;

//Convert Binary to Decimal
void binToDecimal(int n) {
    int res = 0;
    int p = 1;
    while(n > 0) {
        int lastDig = n % 10;
        res += lastDig * p;
        p = p * 2;
        n = n / 10;
    }
    cout << "Decimal form = " << res << "\n";
}

//Convert Decimal to Binary
void decToBinary(int n) {
    int res = 0;
    int p = 1;
    while(n > 0) {
        int rem = n % 2;
        res += rem * p;
        p = p * 10;
        n = n / 2;
    }
    cout << "Binary form = " << res << "\n";
}

int main() {
    binToDecimal(101);
    decToBinary(5);
    return 0;
}



================================================
FILE: 09_Pointers/pointers.cpp
================================================
#include <iostream>
using namespace std;

void passValue(int param) {
    param = 1000;
}

//using Pointers
void passReference(int *param) {
    *param = 1000;
}

//using Reference Variable
void passReference2(int &param) {
    param = 5000;
}

int main() {
    int a = 10;
    int *ptr = &a;
    int **ptr2 = &ptr;

    cout << &a << " = " << ptr << endl;
    cout << &ptr << " = " << ptr2 << endl;

    //Dereference Operator
    cout << a << " = " << *ptr << " = " << *(&a) << endl;

    *ptr = 20;
    cout << a << endl; //should be 20 now

    //Null Pointer
    float* nptr = NULL;
    cout << nptr << endl;

    //cout << *nptr; // Gives Segmentation Fault

    //Pass by value
    int x = 0;
    passValue(x);
    cout << x << endl;

    //Pass by reference
    passReference(&x);
    cout << x << endl;

    //Reference Variable
    int i = 5;
    int &j = i;
    j++;
    cout << i << endl;

    passReference2(x);
    cout << x << endl;
}




================================================
FILE: 10_Array_1/arrays.cpp
================================================
#include <iostream>
using namespace std;

void printArr(int *arr, int n) {
    for(int i=0; i<n; i++) {
        cout << arr[i] << ",";
    }
    cout << endl;
}

int linearSearch(int *arr, int n, int key) {
    for(int i=0; i<n; i++) {
        if(arr[i] == key) {
            return i;
        }
    }

    return -1;
}

void findLargest(int *arr, int n) {
    int max;
    for(int i=0; i<n; i++) {
        if(arr[i] > max) {
            max = arr[i];
        }
    }

    cout << "max = " << max << endl;
}

//copy & paste method
void reverseArr1(int *arr, int n) {
    int newArr[n];
    for(int i=0; i<n; i++) {
        newArr[i] = arr[n-i-1];
    }

    for(int i=0; i<n; i++) {
        arr[i] = newArr[i];
    }

    printArr(arr, n);
}

//2 pointer method
void reverseArr2(int *arr, int n) {
    int start = 0, end = n-1;
    
    while(start < end) {
        swap(arr[start], arr[end]);
        start++;
        end--;
    }

    printArr(arr, n);
}

//Binary Search
int binSearch(int *arr, int n, int key) {
    int start = 0, end = n-1;

    while(start <= end) {
        int mid = (start + end) / 2;

        if(key == arr[mid]) {
            return mid;
        } else if(key > arr[mid]) {
            //search in 2nd half
            start = mid + 1;
        } else {
            //search in 1st half
            end = mid - 1;
        }
    }

    return -1;
}

//Print all Subarrays of an Array
void printSubarrays(int *arr, int n) {
    for(int start=0; start<n; start++) {
        for(int end=start; end<n; end++) {

            for(int i=start; i<=end; i++) {
                cout << arr[i] << ",";
            }
            cout << endl;
        }
    }
}


int main() {
    //Creating an array
    int marks[5];
    cout << marks[0] << ", " << marks[4] << endl;

    int ages[50] = {24, 48, 64};
    cout << ages[0] << "," << ages[49]<< endl;

    float heights[] = {5.5, 4.9, 6.2};
    cout << heights[0] << endl;

    //Size of array
    int a[5];
    int n = sizeof(a) / sizeof(int);
    cout << "size = " << n << endl;

    //Input & Output Array
    int n;
    cin >> n;
    int arr[n];
    for(int i=0; i<n; i++) {
        cin >> arr[i];
    }

    for(int i=0; i<n; i++) {
        cout << arr[i] << ",";
    }
    cout << "\n";

    int arr[] = {1, 2, 3, 4, 5};
    printArr(arr, 5);

    cout << linearSearch(arr, 5, 3) << endl;

    reverseArr1(arr, 5);
    reverseArr2(arr, 5);

    cout << binSearch(arr, 5, 3) << endl;

    printSubarrays(arr, 5);
    return 0;
}




================================================
FILE: 11_Arrays_2/arrays2.cpp
================================================
#include <iostream>
using namespace std;

//max sum subarray (brute force - O(N^3))
int maxSumSubarray(int *arr, int n) {
    int maxSum = INT_MIN; 
    for(int start=0; start<n; start++) {
        for(int end=start; end<n; end++) {
            int sum = 0;
            for(int i=start; i<=end; i++) {
                sum += arr[i];
            }
            maxSum = max(sum, maxSum);
        }
    }

    cout << maxSum << "\n";
    return maxSum;
}

//max sum subarray - O(N^2)
int maxSumSubarray2(int *arr, int n) {
    int maxSum = INT_MIN; 
    for(int start=0; start<n; start++) {
        int sum = 0;
        for(int i=start; i<n; i++) {
            sum += arr[i];
            maxSum = max(sum, maxSum);
        }
    }

    cout << maxSum << "\n";
    return maxSum;
}

//max sum subarray - Kadane's - O(N)
int maxSumSubarray3(int *arr, int n) {
    int currSum = 0;
    int maxSum = INT_MIN; 
    
    for(int i=0; i<n; i++) {
        currSum += arr[i];
        maxSum = max(currSum, maxSum);
        
        if(currSum < 0) {
            currSum = 0;
        }
    }

    cout << maxSum << "\n";
    return maxSum;
}

//Trapping Rainwater
int trap(int *heights, int n) {
    int maxLeft[100000] = {0};
    int maxRight[100000] = {0};

    int maxTillNow = heights[0];
    for(int i=1; i<n; i++) {
        maxLeft[i] = max(maxTillNow, heights[i-1]);
        maxTillNow = max(maxTillNow, heights[i]);
    }

    maxRight[n-1] = 0;
    maxTillNow = heights[n-1];
    for(int i=n-2; i>=0; i--) {
        maxRight[i] = max(maxTillNow, heights[i+1]);
        maxTillNow = max(maxTillNow, heights[i]);
    }

    int water = 0;
    for(int i=0; i<n; i++) {
        int ht = min(maxLeft[i], maxRight[i]) - heights[i];
        if(ht > 0) {
            water += ht;
        }
    }

    cout << "water trapped = " << water << "\n";
    return water;
}

//Buy & Sell Stocks
int maxProfit(int *prices, int n) {
    int bestBuy[100000] = {0};
    bestBuy[0] = INT_MAX;

    for(int i=1; i<n; i++) {
        bestBuy[i] = min(bestBuy[i-1], prices[i-1]);
    }

    int maxProfit = 0;
    for(int i=1; i<n; i++) {
        int currProfit = prices[i] - bestBuy[i];
        maxProfit = max(maxProfit, currProfit);
    }

    cout << "max profit = " << maxProfit << "\n";
    return maxProfit;
}

int main() {
    int arr[] = {2, -3, 6, -5, 4, 2};
    int n = sizeof(arr) / sizeof(int);

    maxSumSubarray(arr, n);
    maxSumSubarray2(arr, n);
    maxSumSubarray3(arr, n);

    int arr2[] = {-1, -2, -3};
    maxSumSubarray3(arr2, 3);

    int heights[] = {4, 2, 0, 6, 3, 2, 5};
    trap(heights, 7);

    int prices[] = {7,1,5,3,6,4};
    maxProfit(prices, 6);
    return 0;    
}




================================================
FILE: 12_Basic_Sorting_Algos/sorting.cpp
================================================
#include <iostream>
using namespace std;

//Print Array
void printArr(int arr[], int n) {
    for(int i=0; i<n; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
}

void printArr(char arr[], int n) {
    for(int i=0; i<n; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
}

void bubbleSort(int arr[], int n) {
    for(int i=0; i<n-1; i++) {
        for(int j=0; j<n-i-1; j++) {
            if(arr[j] > arr[j+1]) {
                swap(arr[j], arr[j+1]);
            }
        }
    }

    printArr(arr, n);
}

void selectionSort(int arr[], int n) {
    for(int i=0; i<n-1; i++) {
        int minIdx = i;
        for(int j=i+1; j<n; j++) {
            if(arr[j] < arr[minIdx]) {
                minIdx = j;
            }
        }

        swap(arr[i], arr[minIdx]);
    }

    printArr(arr, n);
}

void insertionSort(int arr[], int n) {
    for(int i=1; i<n; i++) {
        int curr = arr[i];
        int prev = i-1;
        //sorted part loop - backwards
        while(prev >= 0 && arr[prev] > curr) {
            arr[prev+1] = arr[prev];
            prev--;
        }

        //swap
        swap(arr[prev+1], curr);
    }
    
     printArr(arr, n);
}

void countSort(int arr[], int n) {
    int range = INT_MIN;
    for(int i=0; i<n; i++) {
        range = max(range, arr[i]);
    }

    int freqArr[100001];
    for(int i=0; i<n; i++) {
        freqArr[arr[i]]++;
    }

    for(int i=0; i<range; i++) {
        while(freqArr[i] > 0) {
            arr[i] = i;
            freqArr[i]--;
        }
    }

    printArr(arr, n);
}



void sortChars(char arr[], int n) {
    for(int i=1; i<n; i++) {
        char curr = arr[i];
        int prev = i-1;
        
        while(prev >= 0 && arr[prev] < curr) {
            arr[prev+1] = arr[prev];
            prev--;
        }

        swap(arr[prev+1], curr);
    }
    
     printArr(arr, n);
}

int main() {
    int arr[5] = {5, 4, 1, 3, 2};
    //bubbleSort(arr, 5);
    //selectionSort(arr, 5);
    //insertionSort(arr, 5);

    int arr2[8] = {1, 4, 1, 3, 2, 4, 3, 7};
    //countSort(arr2, 8);

    sort(arr2, arr2+8);
    printArr(arr2, 8);

    char ch[] = { 'f', 'b', 'a', 'e', 'c', 'd'};
    sortChars(ch, 6);
    
    return 0;    
}




================================================
FILE: 13_2DArray/2DArrays.cpp
================================================
#include <iostream>
using namespace std;

void printSpiral(int matrix[][4], int n, int m) {
    int scol = 0, srow = 0;
    int ecol = m-1, erow = n-1;

    while(srow <= erow && scol <= ecol) {
        //top
        for(int j=scol; j<=ecol; j++) {
            cout << matrix[srow][j] << " ";
        }

        //right
        for(int i=srow+1; i<=erow; i++) {
            cout << matrix[i][ecol] << " ";
        }

        //bottom
        for(int j=ecol-1; j>=scol; j--) {
            if(srow == erow) {
                break;
            }
            cout << matrix[erow][j] << " ";
        }

        //left
        for(int i=erow-1; i>=srow+1; i--) {
            if(scol == ecol) {
                break;
            }
            cout << matrix[i][scol] << " ";
        }

        srow++; scol++;
        erow--; ecol--;
    }

    cout << endl;
}

void diagonalSum(int mat[][4], int n) { 
    int sum = 0;

    //O(n^2)
    for(int i=0; i<n; i++) {
        for(int j=0; j<n; j++) {
            if(i == j) {
                sum += mat[i][j];
            } else if (i+j == n-1) {
                sum += mat[i][j];
            }
        }
    }
    cout <<"O(N^2) code => sum = " << sum << endl;

    //O(n)
    sum = 0;
    for(int i=0; i<n; i++) {
        sum += mat[i][i];
        if(n-1-i != i)
            sum+= mat[i][n-1-i];
    }
    cout <<"O(N) code => sum = " << sum << endl;
}

bool search(int mat[][4], int n, int m, int key) {
    int i=0, j=m-1;
    while(i < n && j >= 0) {
        if(mat[i][j] == key) {
            cout << "found at (" << i << "," << j << ")\n";
            return true;
        } else if(mat[i][j] > key) {
            //go left
            j--;
        } else {
            //go right
            i++;
        }
    }

    cout << "key NOT found\n";
    return false;
}

void func(int (*ptr)[4]) {
    cout << ptr << endl;
    cout << ptr+1 << endl;

    //address(pointer) of row
    cout << "0th row address" << ptr << endl;
    cout << "1st row address" << (ptr+1) << endl;

    //actual row
    cout << "0th row start" << *ptr << endl;
    cout << "1st row start" << *(ptr+1) << endl;

    //to get j=2 column in i=0 row
    cout << "(0, 2) = " << *(*ptr+2) << endl;

    //to get j=2 column in i=1 row
    cout << "(1, 2) = " << *(*(ptr+1)+2) << endl;

}

int main() {
    int matrix[4][4] = {{1, 2, 3, 4}, 
                         {5, 6, 7, 8},
                         {9, 10, 11, 12},
                         {13, 14, 15, 16}};

    int matrix2[3][4] = {{1, 2, 3, 4}, 
                         {5, 6, 7, 8},
                         {9, 10, 11, 12}};

    printSpiral(matrix, 4, 4);
    //Expected : 1 2 3 4 8 12 16 15 14 13 9 5 6 7 11 10

    printSpiral(matrix2, 3, 4);

    diagonalSum(matrix, 4);

    int mat[4][4] = {{10, 20, 30, 40}, 
                     {15, 25, 35, 45},
                     {27, 29, 37, 48},
                     {32, 33, 39, 50}};

    search(mat, 4, 4, 33);
    search(mat, 4, 4, 100);

    //Pointers & 2D Arrays
    func(matrix);
    return 0;    
}




================================================
FILE: 14_String/strings.cpp
================================================
#include <iostream>
#include <cstring>
#include <string>
using namespace std;

//Convert to UpperCase
void toUpper(char str[], int n) {
    for(int i=0; i<n; i++) {
        if(str[i] >= 'A' && str[i] <= 'Z') {
            continue;
        } else {
            int diff =  str[i] - 'a';
            str[i] = 'A' + diff;
        }
    }
}

//Reverse of a char Array
void reverse(char str[], int n) {
    int st = 0, end = n-1;

    while(st < end) {
        swap(str[st++], str[end--]);
    }
}

//Valid Palindrome
bool isValid(char str[], int n) {
    int st = 0, end = n-1;

    while(st < end) {
        if(str[st++] != str[end--]) {
            cout << "not valid";
            return false;
        }
    }
    cout << "valid";
    return true;
}

//Valid Anagram
bool isAnagram(string s, string t) {
        if(s.length() != t.length()) {
            return false;
        }

        int count[26] = {0};
        for(int i=0; i<s.length(); i++) {
            count[s[i]-'a']++;
        }

        for(int i=0; i<t.length(); i++) {
            int idx = t[i] - 'a';
            if(count[idx] == 0) {
                return false;
            }
            count[idx]--;
        }

        return true;
}

int main() {
    //C++ char arrays
    /*char word[20];
    cin.getline(word, 20);
    cout << "your word is : " << word << endl;*/
    
    //<cstring> functions
    /*strcpy(word, "c++");
    cout << "now your word is : " << word << endl;

    strcat(word, " is my favorite");
    cout << word << endl;

    cout << strcmp("hello", "hello") << endl;
    cout << strcmp("abc", "xyz") << endl;*/

    //C++ Strings
    string str;
    getline(cin, str);
    cout << str << endl;

    //String Member Functions
    cout << str.length() << endl;
    cout << str.at(0) << endl;
    cout << str.substr(2, 3) << endl;
    cout << str.find("college") << endl;
    cout << str.find("xyz") << endl;
    return 0;    
}




================================================
FILE: 15_Vector/vectors.cpp
================================================
#include <iostream>
#include <vector>
using namespace std;

// Pair Sum
vector<int> twoSum(vector<int>& nums, int target) {
        int st = 0, end = nums.size()-1;
        vector<int> ans;

        while(st < end) {
            int sum = nums[st] + nums[end];
            if(sum == target) {
                ans.push_back(st+1);
                ans.push_back(end+1);
                break;
            } else if(sum > target) {
                end--;
            } else {
                st++;
            }
        }

        return ans;
}

int main() {
    //Dynamic Allocation & Deallocation
    //Example - 1
    int *ptr = new int;
    *ptr = 100;
    cout << *ptr << endl;
    delete ptr;
    
    //1D Dynamic Array
    int size;
    cout << "enter size of array : ";
    cin >> size;
    int *arr = new int[size];

    for(int i=0; i<size; i++) {
        arr[i] = i+1;
        cout << arr[i] << " ";
    }
    cout << endl;

    delete[] arr;

    //2D Dynamic Array
    int rows, cols;
    cout << "enter rows : ";
    cin >> rows;
    cout << "enter cols : ";
    cin >> cols;

    int **matrix = new int*[rows];
    for(int i=0; i<rows; i++) {
        matrix[i] = new int[cols];
    }

    int x = 1;
    for(int i=0; i<rows; i++) {
        for(int j=0; j<cols; j++) {
            matrix[i][j] = x++;
            cout << matrix[i][j] << " ";
        }
        cout << endl;
    }

    //vectors
    vector<int> vec1;

    vector<int> vec2 = {1, 2, 3, 4};

    vector<int> vec3(5, -1);

    vector<int> vec = {1, 2, 3, 4};
    cout << vec.size() << endl;
    cout << vec.capacity() << endl;

    //print elements
    for(int i=0; i<vec.size(); i++) {
        cout << vec[i] << " ";
    }
    cout << endl;

    vec.push_back(5);
    cout << vec.capacity() << endl;

    //2D Vector
    vector<vector<int>> matrix = {{1}, {2, 3}, {4, 5, 6}};

    for(int i=0; i<matrix.size(); i++) {
        for(int j=0; j<matrix[i].size(); j++) {
            cout << matrix[i][j] << " ";
        }
        cout << endl;
    }


    return 0;    
}




================================================
FILE: 16_Bit_Manipulation/bit_manip.cpp
================================================
#include <iostream>
#include <vector>
using namespace std;

bool isPowerOf2(int num) {

    if((num & (num-1)) == 0) {
        return true;
    } else {
        return false;
    }
}

void updateIthBit(int num, int i, int val) {
    num = num & ~(1 << i);

    int mask = val << i;
    num = num | mask;

    cout << num << endl;
}

void clearLastIBits(int num, int i) {
    int mask = (~0) << i;
    num = num & mask;

    cout << num << endl;
}

void clearBitsInRange(int num, int i, int j) {
    int a = (~0) >> (j+1);
    int b = (1 << i) - 1;
    int mask = a | b;
    num = num & mask;

    cout << num << endl;
}

int countSetBits(int num) {
    int count = 0;
    
    while(num > 0) {
        if(num & 1) {
            count++;
        }
        num = num >> 1;
    }

    cout << count << endl;
    return count;
}

//calculate x^n
int fastExponentiation(int x, int n) {
    int ans = 1;

    while(n > 0) {
        int lastBit = n & 1;
        if(lastBit)
            ans = ans * x;

        x = x*x;
        n = n >> 1;
    }

    cout << ans << endl;
    return ans;
}

int main() {
    /* Binary Operators - AND, OR, XOR */
    int x = 3, y = 5;
    
    cout << (x & y) << endl;
    cout << (x | y) << endl;
    cout << (x ^ y) << endl;

    //Binary NOT
    cout << ~0 << endl;
    cout << ~6 << endl;

    //Binary Shift
    cout << (7 << 2) << endl;// same as (7 * 2^2)
    cout << (7 >> 2) << endl;// same as (7 / 2^2)

    //Practice Qs
    cout << ~4 << endl;
    cout << (8 >> 1) << endl;

    //Odd or Even
    int num = 7;
    bool isOdd = num & 1;
    cout << (isOdd ? "odd" : "even") << endl;

    //Get ith bit
    num = 6;
    int i = 2;
    int mask = 1 << i;
    if(num & mask) {
        cout << "bit is 1\n";
    } else {
        cout << "bit is 0\n";
    }

    //Set ith bit
    num = 6;
    i = 3;
    mask = 1 << i;
    num = num | mask;
    cout << num << endl; //14 is expected;

    //Clear ith Bit
    num = 6;
    i = 1;
    mask = ~(1 << i);
    num = num & mask;
    cout << num << endl; //4 is expected; 

    //Power of 2
    cout << isPowerOf2(8) << endl;
    cout << isPowerOf2(7) << endl;

    //Update ith Bit
    updateIthBit(7, 2, 0);
    updateIthBit(7, 3, 1);

    //Clear last i bits
    clearLastIBits(15, 2);

    //Count Set Bits;
    countSetBits(10);
    countSetBits(7);

    //Fast Exponentiation
    fastExponentiation(3, 4);
    return 0;    
}




================================================
FILE: 17_OOPS1/oops1.cpp
================================================
#include <iostream>
#include <string>
using namespace std;

class Student {
private:
    float cgpa;

public:
    string name;

    //Setter
    void setCgpa(float newCgpa) {
        if(newCgpa < 0) {
            cout << "Invalid Data\n";
            return;
        }
        cgpa = newCgpa;
    }

    //Getter
    float getCgpa() {
        return cgpa;
    }

    void getPercentage() {
        cout << (cgpa * 10) << "% \n";
    }
};

class Car {
    string name;
    int price;

public:
    int *mileage;
    //Contructor
    Car() {
        cout << "Creating & Initializing a new car..\n";
    }

    //Parameterized Contructor
    Car(string name, int price) {
        cout << "Creating & Initializing a new car..\n";
        this->name = name;
        this->price = price;
        mileage = new int;
        *mileage = 12;
    }

    //Custom Copy Constructor
    Car(Car &original) {
        cout << "copying..\n";
        name = original.name;
        price = original.price;
        mileage = new int;
        *mileage = *original.mileage;
    }

    //Getter
    string getName() {
        return name;
    }

    int getPrice() {
        return price;
    }

    int getMileage() {
        return *mileage;
    }

    //Setter
    // void setMileage(int mileage) {
    //     mileage = &mileage;
    // }

    ~Car() {
        cout << "object deletion..\n";
        if(mileage != NULL) {
            delete mileage;
            mileage = NULL;
        }
    }
};

//Inheritance
class Animal {
    string color;

public: 
    void eat() {
        cout << "eats\n";
    }

    void breathe() {
        cout << "breathes\n";
    }
};

class Fish : public Animal {
    int fins;

public:
    void swim() {
        cout << "swims\n";
    }
};

int main() {
    // Student s1;
    // cout << sizeof(s1) << endl;
    // s1.name = "shradha";
    // cout << s1.name << endl;

    // //Setter
    // s1.setCgpa(9.0);

    // //Getter
    // cout << s1.getCgpa() << endl;
    // s1.getPercentage();

    //Contructors
    // Car c1("maruti 800", 4);
    // cout << c1.getName() << endl;
    // cout << c1.getMileage() << endl;


    //Default Copy Constructor
    // Car c2(c1);
    // cout << "**************\n";
    // cout << c1.getName() << endl;
    // cout << c1.getPrice() << endl;
    // cout << c2.getMileage() << endl;

    // *c2.mileage = 15;
    // cout << c2.getMileage() << endl;
    // cout << c1.getMileage() << endl;

    //Inheritance
    Fish f1;
    f1.eat();
    f1.swim();
    return 0;    
}




================================================
FILE: 18_OOPS2/oops2.cpp
================================================
#include <iostream>
#include <string>
using namespace std;

//Function Overloading
class Print {
public:
    void show(int x) {
        cout << "int : " << x << endl;
    }

    void show(string str) {
        cout << "string : " << str << endl;
    }
};

//Operator Overloading
class Complex {
    int real;
    int img;

public:
    Complex(int r, int i) {
        real = r;
        img = i;
    }

    void showNum() {
        cout << real << " + " <<  img << "i\n";
    }

    Complex operator - (Complex &obj) {
        int resReal = this->real - obj.real;
        int resImg = this->img - obj.img;
        Complex res(resReal, resImg);
        return res;
    }

    Complex operator + (Complex &obj) {
        int resReal = this->real + obj.real;
        int resImg = this->img + obj.img;
        Complex res(resReal, resImg);
        return res;
    }
};

//Function Overriding & Virtual Function
class Parent {
public:
    void show() {
        cout << "parent show\n";
    }

    virtual void hello() {
        cout << "hello from parent\n";
    }
};

class Child : public Parent {
public:
    void show() {
        cout << "child show\n";
    }  

    void hello() {
        cout << "hello from child\n";
    }
};

//Abstract Classes & Pure Virtual Functions

class Shape {
    //This is an abstract class
public:
    virtual void draw() = 0; //Pure Virtual Function
};

class Square : public Shape {
public:
    void draw() {
        cout << "drawing a rectangle\n";
    }
};

class Circle : public Shape {
public:
    void draw() {
        cout << "drawing a circle\n";
    }
};

//Static 
void counter() {
    static int count = 0;
    count++;
    cout << "count : " << count << endl;
}

class Example {
public:
    Example() {
        cout << "constructor\n";
    }

    ~Example() {
        cout << "destructor\n";
    }
};

//Friend Class & Function
class A {
    string secret = "private secret";
    friend class B;
    friend void shareSecret(A &obj);
};

class B {
public:
    void showSecret(A &obj) {
        cout << obj.secret << endl;
    }
};

void shareSecret(A &obj) {
        cout << obj.secret << endl;
}

int main() {
    Print p1;
    p1.show(50);
    p1.show("apnacollege");
    
    Complex num1(1, 2);
    Complex num2(3, 4);
    Complex res = num1 + num2;
    res.showNum();

    Child c1;
    c1.show();
    
    Child c2;
    Parent *par1;
    par1 = &c2; //Binding at runtime
    par1->hello();
    
    Circle cir1;
    Square squ1;
    cir1.draw();
    squ1.draw();

    counter();
    counter();
    counter();

    //Static object
    int x = 0;
    if(x == 0) {
        static Example eg1;
    }
    cout << "exiting main function.\n";

    A a1;
    B b1;
    b1.showSecret(a1);
    shareSecret(a1);
    return 0;    
}




================================================
FILE: 19_Recursion1/recursion1.cpp
================================================
#include <iostream>
#include <string>
#include <vector>
using namespace std;

//Simple Recursive Function with Stack Overflow
void func() {
    cout << "function call\n";
    func();
}

//Factorial 
int factorial(int n) {
    if(n == 1) {
        return 1;
    }
    return n * factorial(n-1);
}

//Print Decreasing
void print(int n) {
    if(n == 0) {
        return;
    }

    cout << n << " ";
    print(n-1);
}

//Sum of N Natural Numbers
int sum(int n) {
    if(n == 1) {
        return 1;
    }

    return n + sum(n-1);
}

//Nth Fibonacci
int fibonacci(int n) {
    if(n == 0 || n == 1) {
        return n;
    }

    return fibonacci(n-1) + fibonacci(n-2);
}

//Is Array Sorted
bool isSorted(int arr[], int i, int n) {
    if(i == n-1) {
        return true;
    }

    if(arr[i] > arr[i+1]) {
        return false;
    }

    return isSorted(arr, i+1, n);
}

//First Occurrence
int firstOccur(vector<int> vec, int target, int i) {
    if(i == vec.size()) {
        return -1;
    }

    if(vec[i] == target) {
        return i;
    }

    return firstOccur(vec, target, i+1);
}

//Last Occurrence
int lastOccur(vector<int> vec, int target, int i) {
    if(i == vec.size()) {
        return -1;
    }

    int idxFound = lastOccur(vec, target, i+1);
    
    if(idxFound == -1 && vec[i] == target) {
        return i;
    }

    return idxFound;
}

//X^N
int pow(int x, int n) {
    if(n == 0) {
        return 1;
    }

    int halfPow = pow(x, n/2);
    int halfPowSquare = halfPow * halfPow;
    if(n % 2 == 0) {
        //even
        return halfPowSquare;
    } else {
        return x * halfPowSquare;
    }
}

int main() {
    cout << factorial(5) << endl;

    print(6);
    cout << endl;

    cout << sum(5) << endl;

    cout << fibonacci(6) << endl;

    int arr1[5] = {1, 2, 3, 4, 5};
    int arr2[5] = {1, 2, 4, 3, 5};
    cout << isSorted(arr1, 0, 5) << endl;
    cout << isSorted(arr2, 0, 5) << endl;

    vector<int> vec = {1, 2, 3, 3, 3, 4};
    cout << firstOccur(vec, 3, 0) << endl;
    cout << lastOccur(vec, 3, 0) << endl;

    cout << pow(2, 10) << endl;
    return 0;    
}




================================================
FILE: 20_Recursion2/rec2.cpp
================================================
#include <iostream>
#include <string>
using namespace std;

//Tiling Problem
int countWays(int n) {
    if(n == 0 || n == 1) {
        return 1;
    }

    //vertical choice
    int ways1 = countWays(n-1);

    //horizonal choice
    int ways2 = countWays(n-2);

    return ways1 + ways2;
}

//Remove Duplicates
void removeDuplicates(string str, int i, bool map[26], string ans) {
    if(i == str.length()) {
        cout << "ans : " << ans << endl;
        return;
    }

    int mapIdx = (int)(str.at(i) - 'a');

    if(map[mapIdx]) {
        removeDuplicates(str, i+1, map, ans);
    } else {
        map[mapIdx] = true;
        removeDuplicates(str, i+1, map, ans+str.at(i));
    }
    
}

//Friends Pairing Problem
int pairFriends(int n) {
    if(n == 1 || n == 2) {
        return n;
    }

    return pairFriends(n-1) + (n-1) * pairFriends(n-2);
}

//Binary Strings Problem
void binStrings(int n, string ans, int lastPlace) {
    if(n == 0) {
        cout << ans << endl;
        return;
    }

    binStrings(n-1, ans+'0', 0);

    if(lastPlace != 0) {
        binStrings(n-1, ans+'1', 1);
    }
}

void binStrings(int n, string ans) {
    if(n == 0) {
        cout << ans << endl;
        return;
    }

    binStrings(n-1, ans+'0');

    if(ans[ans.size()-1] != '1') {
        binStrings(n-1, ans+'1');
    }
}

int main() {
    cout << countWays(4) << endl;

    string ans = "";
    bool map[26] = {false};
    removeDuplicates("appnnacollege", 0, map, ans); //apncoleg

    cout << pairFriends(3) << endl;

    ans = "";
    //binStrings(3, ans, 0);

    binStrings(3, ans);
    return 0;    
}




================================================
FILE: 21_Divide_and_Conquer/divideAndConquer.cpp
================================================
#include <iostream>
#include <vector>
using namespace std;

void printArr(int arr[], int n) {
    for(int i=0; i<n; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
}

void merge(int arr[], int si, int mid, int ei) {
    vector<int> temp;
    int i=si, j=mid+1;

    while(i <= mid && j <= ei) {
        if(arr[i] <= arr[j]) {
            temp.push_back(arr[i++]);
        } else {
            temp.push_back(arr[j++]);
        }
    }

    while(i <= mid) {
        temp.push_back(arr[i++]);
    } 

    while(j <= ei) {
        temp.push_back(arr[j++]);
    }

    //copy back to original
    for(int idx=si, x=0; idx<=ei; idx++) {
        arr[idx] = temp[x++];
    }    
}

void mergeSort(int arr[], int si, int ei) {
    if(si >= ei) {
        return;
    }

    int mid = si + (ei - si)/2;
    mergeSort(arr, si, mid);
    mergeSort(arr, mid+1, ei);
    
    merge(arr, si, mid, ei);
}

int partition(int arr[], int si, int ei) {
    int pivot = arr[ei];
    int i=si-1;

    for(int j=si; j<ei; j++) {
        if(arr[j] <= pivot) {
            i++;
            swap(arr[i], arr[j]);
        }
    }

    i++;
    swap(arr[i], arr[ei]);

    return i;
}

void quickSort(int arr[], int si, int ei) {
    if(si >= ei) {
        return;
    }

    int pivotIdx = partition(arr, si, ei);
    quickSort(arr, si, pivotIdx-1); //left
    quickSort(arr, pivotIdx+1, ei); //right
}

int search(int arr[], int si, int ei, int tar) {
    if(si > ei) {
        return -1;
    }

    int mid = si + (ei - si)/2;

    if(arr[mid] == tar) {
        return mid;
    }

    if(arr[si] <= arr[mid]) { //Line 1
        if(arr[si] <= tar && tar <= arr[mid]) {
            //go left
            return search(arr, si, mid-1, tar);
        } else {
            //go right
            return search(arr, mid+1, ei, tar);
        }
    } else {
        //Line2
        if(tar >= arr[mid] && tar <= arr[ei]) {
            //go right
            return search(arr, mid+1, ei, tar);
        } else {
            //go left
            return search(arr, si, mid-1, tar);
        }
    }
}

int main() {
    int arr[6] = {6, 3, 7, 5, 2, 4};
    int n = 6;
    
    //mergeSort(arr, 0, n-1);

    quickSort(arr, 0, n-1);
    printArr(arr, n);

    int arr2[7] = {4, 5, 6, 7, 0, 1, 2};
    int tar = 0;
    cout << "idx : " << search(arr2, 0, 6, tar) << endl;
    return 0;    
}




================================================
FILE: 24_Backtracking/backtracking.cpp
================================================
#include <iostream>
#include <string>
#include <vector>
using namespace std;

void printArr(int arr[], int n) {
    for(int i=0; i<n; i++) {
        cout << arr[i] << " ";
    }

    cout << endl;
}

void changeArr(int arr[], int n, int i) {
    if(i == n) {
        printArr(arr, n);
        return;
    }

    arr[i] = i+1;
    changeArr(arr, n, i+1);
    arr[i] -= 2;
}

void allSubsets(string str, int i, string subset) {
    if(i == str.size()) {
        cout << subset << endl;
        return;
    }

    char ch = str[i];
    allSubsets(str, i+1, subset);
    allSubsets(str, i+1, subset+ch);
}

void allPermutations(string str, string ans) {
    if(str.size() == 0) {
        cout << ans << endl;
        return;
    }

    for(int i=0; i<str.size(); i++) {
        string newStr = str.substr(0, i) + str.substr(i+1, i+str.size());
        allPermutations(newStr, ans+str[i]);
    }
}

void printBoard(vector<vector<char>> board) {
    int n = board.size();
    for(int i=0; i<n; i++) {
        for(int j=0; j<n; j++) {
            cout << board[i][j] << " ";
        }
        cout << endl;
    }

    cout << "---------------\n";
}

bool isSafe(vector<vector<char>> board, int row, int col) {
    int n = board.size();
    //vertical
    for(int j=0; j<col; j++) {
        if(board[row][j] == 'Q') {
            return false;
        }
    }

    //horizontal
    for(int i=0; i<row; i++) {
        if(board[i][col] == 'Q') {
            return false;
        }
    }

    //diagonal left
    for(int i=row-1, j=col-1; i>=0 && j>=0; i--, j--) {
        if(board[i][j] == 'Q') {
            return false;
        }
    }

    //diagonal right
    for(int i=row-1, j=col+1; i>=0 && j<n; i--, j++) {
        if(board[i][j] == 'Q') {
            return false;
        }
    }
    return true;
}


int nQueens(vector<vector<char>> board, int row) {
    int n = board.size();
    if(row == n) {
        printBoard(board);
        return 1;
    }

    int count = 0;
    for(int j=0; j<n; j++) {
        if(isSafe(board, row, j)) {
            board[row][j] = 'Q';
            count += nQueens(board, row+1);
            board[row][j] = '.';
        }
    }

    return count;
}

int gridWays(int i, int j, int n, int m) {
    if(i == n-1 && j == m-1) {
        return 1;
    }

    if(i >= n || j >= m) {
        return 0;
    }

    int totWays = 0;
    
    //go right
    totWays += gridWays(i, j+1, n, m);

    //go down
    totWays += gridWays(i+1, j, n, m);

    return totWays;
}

bool isSafe(int sudoku[9][9], int row, int col, int val) {
    //same col
    for(int i=0; i<9; i++) {
        if(sudoku[i][col] == val) {
            return false;
        }
    }

     //same row
    for(int j=0; j<9; j++) {
        if(sudoku[row][j] == val) {
            return false;
        }
    }

    //same 3x3 grid
    int sr = (row/3) * 3;
    int sc = (col/3) * 3;

    for(int i=sr; i<sr+3; i++) {
        for(int j=sc; j<sc+3; j++) {
            if(sudoku[i][j] == val) {
                return false;
            }
        }
    }

    return true;
}

bool sudokuSolver(int sudoku[9][9], int row, int col) {
    cout << "row = " << row << " , col = " << col << endl;
    if(row == 9) {
        for(int i=0; i<9; i++) {
            for(int j=0; j<9; j++) {
                cout << sudoku[i][j] << " ";
            }
            cout << endl;
        }

        return true;
    } 

    int nextRow = row;
    int nextCol = col + 1;

    if(nextCol == 9) {
        nextRow = row+1;
        nextCol = 0;
    }

    if(sudoku[row][col] != 0) {
        return sudokuSolver(sudoku, nextRow, nextCol);
    }

    for(int digit=1; digit<=9; digit++) {
        if(isSafe(sudoku, row, col, digit)) {
            sudoku[row][col] = digit;
            if(sudokuSolver(sudoku, nextRow, nextCol)) {
                return true;
            }
            sudoku[row][col] = 0;
        }
    }

    return false;
}

int main() {
    int arr[5];
    int n = 5;
    changeArr(arr, n, 0);
    printArr(arr, n);

    string str = "abc";
    string ans = "";
    allSubsets(str, 0, ans);
    cout << "--------------------------\n";

    allPermutations(str, ans);
    cout << "--------------------------\n";

    int n = 4;
    vector<vector<char>> board;
    
    for(int i=0; i<n; i++) {
        vector<char> newRow;
        for(int j=0; j<n; j++) {
            newRow.push_back('.');
        }
        board.push_back(newRow);
    }

    int count = nQueens(board, 0);
    cout << "total ways : " << count << endl;

    
    cout << gridWays(0, 0, 3, 3) << endl;

    int sudoku[9][9] = {{0, 0, 8, 0, 0, 0, 0, 0, 0}, 
                        {4, 9, 0, 1, 5, 7, 0, 0, 2},
                        {0, 0, 3, 0, 0, 4, 1, 9, 0},
                        {1, 8, 5, 0, 6, 0, 0, 2, 0},
                        {0, 0, 0, 0, 2, 0, 0, 6, 0},
                        {9, 6, 0, 4, 0, 5, 3, 0, 0},
                        {0, 3, 0, 0, 7, 2, 0, 0, 4},
                        {0, 4, 9, 0, 3, 0, 0, 5, 7},
                        {8, 2, 7, 0, 0, 9, 0, 1, 3}};

    sudokuSolver(sudoku, 0, 0);
    return 0;    
}




================================================
FILE: 25_LinkedList1/ll1.cpp
================================================
#include <iostream>
using namespace std;

class Node {
public:
    int data;
    Node* next;

    Node(int data) {
        this->data = data;
        next = NULL;
    }

    ~Node() {
        if(next != NULL) {
            delete next;
            next = NULL;
        }
    }
};

class List {
    Node* head;
    Node* tail;

public:
    List() {
        head = NULL;
        tail = NULL;
    }

    void push_front(int val) {
        Node* newNode = new Node(val);

        if(tail == NULL) {
            head = tail = newNode;
        } else {
            newNode->next = head;
            head = newNode;
        }
    }

    void push_back(int val) {
        Node* newNode = new Node(val);

        if(tail == NULL) {
            head = tail = newNode;
        } else {
            tail->next = newNode;
            tail = newNode;
        }
    }

    void printList() {
        Node* temp = head;
        while(temp != NULL) {
            cout << temp->data << " -> ";
            temp = temp->next;
        }
        cout << "NULL\n";
    }

    void insert(int val, int pos) {
        if(pos == 0) {
            push_front(val);
            return;
        }

        Node* temp = head;
        int i=0;
        while(temp != NULL && i<pos-1) {
            temp = temp->next;
            i++;
        }

        if(temp == NULL) {
            cout << "Invalid position\n";
            return;
        }

        Node* newNode = new Node(val);
        newNode->next = temp->next;
        temp->next = newNode;
    }

    void pop_front() {
        if(head == NULL) {
            return;
        }

        Node* temp = head;
        head = head->next;
        
        temp->next = NULL;
        delete temp;
    }

    void pop_back() {
        if(head == NULL) { //0 els
            return;
        }
        if(head->next == NULL) { //1 el
            delete head;
            head = NULL;
            return;
        }

        Node* temp = head;
        while(temp->next->next != NULL) {
            temp = temp->next;
        }
        //temp has tail's prev
        temp->next = NULL;
        
        delete tail;
        tail = temp;
    }

    ~List() {
        if(head != NULL) {
            delete head; 
            head = NULL; 
        }
    }

    int searchItr(int key) {
        Node* temp = head;
        int idx = 0;

        while(temp != NULL) {
            if(temp->data == key) {
                return idx;
            }
            temp = temp->next;
            idx++;
        }
        
        return -1;
    }

    int searchRec(int key) {
        return searchHelper(head, key);
    }

    int searchHelper(Node* h, int key) {
        if(h == NULL) {
            return -1;
        }

        if(h-> data == key) {
            return 0; //current idx
        }

        int ans = searchHelper(h->next, key);
        if(ans == -1) {
            return -1;
        }

        return ans + 1;
    }

    void reverseLL() {
        Node* prev = NULL;
        Node* curr = head;

        while(curr != NULL) {
            Node* next = curr->next;
            curr->next = prev;

            prev = curr;
            curr = next;
        }

        head = prev;
    }

    int sizeLL() {
        Node* temp = head;
        int sz = 0;

        while(temp != NULL) {
            temp = temp->next;
            sz++;
        }
        return sz;
    }

    void removeNth(int n) {
        int size = sizeLL();
        cout << "size : " << size << endl;
        if(n == size) {
            pop_front();
            return;
        }

        Node* temp = head;
        for(int i=1; i<size-n; i++) {
            temp = temp->next;
        }

        Node* toDel = temp->next; //node to delete
        temp->next = temp->next->next;
    }
}; 

int main() {
        List ll;

        ll.push_front(5);
        ll.push_front(4);
        ll.push_front(3);
        ll.push_front(2);
        ll.push_front(1);

       ll.printList();
       ll.removeNth(2); //delete 4
       ll.printList();
       return 0;
}








================================================
FILE: 26_LinkedList2/doubly_linkedlist.cpp
================================================
#include <iostream>
using namespace std;

class Node {
public:
    int data;
    Node* next;
    Node* prev;

    Node(int data) {
        this->data = data;
        next = prev = NULL;
    }
};

class DoublyList {
public:
    Node* head;
    Node* tail;

    DoublyList() {
        head = NULL;
        tail = NULL;
    }

    void push_front(int val) {
        Node* newNode = new Node(val);
        if(head == NULL) {
            head = tail = newNode;
        } else {
            head->prev = newNode;
            newNode->next = head;
            head = newNode;
        }
    }

    void printList() {
        Node* temp = head;
        while(temp != NULL) {
            cout << temp->data << " <=> ";
            temp = temp->next;
        }
        cout << "NULL" << endl;
    }

    void pop_front() {
        cout << "deleting : " << head->data << endl;
        Node* temp = head;
        head = head->next;
        if(head != NULL) {
            head->prev = NULL;
        }
        temp->next = NULL;
        delete temp;
    }

    
};

int main() {
    DoublyList dll;
    
    dll.push_front(3);
    dll.push_front(2);
    dll.push_front(1);

    dll.printList();

    dll.pop_front();
    dll.printList();
}

================================================
FILE: 26_LinkedList2/linkedlist.cpp
================================================
#include <iostream>
#include <string>
#include <vector>
using namespace std;

class Node {
public:
    int data;
    Node* next;

    Node(int data) {
        this->data = data;
        next = NULL;
    }

    // ~Node() {
    //     if(next != NULL) {
    //         delete next;
    //         next = NULL;
    //     }
    // }
};

class List {
public:
    Node* head;
    Node* tail;

    List() {
        head = NULL;
        tail = NULL;
    }

    void push_front(int val) {
        Node* newNode = new Node(val);

        if(tail == NULL) {
            head = tail = newNode;
        } else {
            newNode->next = head;
            head = newNode;
        }
    }

    void push_back(int val) {
        Node* newNode = new Node(val);

        if(head == NULL) {
            head = tail = newNode;
        } else {
            tail->next = newNode;
            tail = newNode;
        }
    }

    void printList() {
        Node* temp = head;
        while(temp != NULL) {
            cout << temp->data << " -> ";
            temp = temp->next;
        }
        cout << "NULL\n";
    }

    void insert(int val, int pos) {
        if(pos == 0) {
            push_front(val);
            return;
        }

        Node* temp = head;
        int i=0;
        while(temp != NULL && i<pos-1) {
            temp = temp->next;
            i++;
        }

        if(temp == NULL) {
            cout << "Invalid position\n";
            return;
        }

        Node* newNode = new Node(val);
        newNode->next = temp->next;
        temp->next = newNode;
    }

    void pop_front() {
        if(head == NULL) {
            return;
        }

        Node* temp = head;
        head = head->next;
        
        temp->next = NULL;
        delete temp;
    }

    void pop_back() {
        if(head == NULL) { //0 els
            return;
        }
        if(head->next == NULL) { //1 el
            delete head;
            head = NULL;
            return;
        }

        Node* temp = head;
        while(temp->next->next != NULL) {
            temp = temp->next;
        }
        //temp has tail's prev
        temp->next = NULL;
        
        delete tail;
        tail = temp;
    }

    // ~List() {
    //     if(head != NULL) {
    //         delete head; 
    //         head = NULL; 
    //     }
    // }  
};

//cycle detection
bool isCycle(Node* head) {
    Node* slow = head;
    Node* fast = head;

    while(fast != NULL && fast->next != NULL) {
        slow = slow->next;
        fast = fast->next->next;

        if(slow == fast) {
            return true;
        }
    }

    return false;
}

void removeCycle(Node* head) {
    Node* slow = head;
    Node* fast = head;
    bool isCycle = false;

    while(fast != NULL && fast->next != NULL) {
        slow = slow->next;
        fast = fast->next->next;

        if(slow == fast) {
            isCycle = true;
            break;
        }
    }

    if(!isCycle) {
        return;
    }

    //Removing Loop
    slow = head;

   if(slow == fast) { 
    //special case when tail is connected to head
        while(fast->next != slow) {
            fast = fast->next;
        }
        fast->next = NULL;

   } else {
        Node* prev = fast;
        while(slow != fast) {
            prev = fast;
            slow = slow->next;
            fast = fast->next;
        }

        //prev is the last node
        prev->next = NULL;
   }
}

Node* splitAtMid(Node* head) {
    Node* slow = head;
    Node* fast = head;
    Node* prev = NULL;

    while(fast != NULL && fast->next != NULL) {
        prev = slow;
        slow = slow->next;
        fast = fast->next->next;
    }

    if(prev != NULL) {
        prev->next = NULL;
    }

    return slow;
}

Node* merge(Node* h1, Node*h2) {
    List ans;
    Node* i = h1;
    Node* j = h2;

    while(i != NULL && j != NULL) {
        if(i->data <= j->data) {
            ans.push_back(i->data);
            i = i->next;
        } else {
            ans.push_back(j->data);
            j = j->next;
        }
    }

    while(i != NULL) {
        ans.push_back(i->data);
        i = i->next;
    }

    while(j != NULL) {
        ans.push_back(j->data);
        j = j->next;
    }
    return ans.head;
}

Node* mergeSort(Node* head) {
    if(head == NULL || head->next == NULL) {
        return head;
    }

    Node* rightHead = splitAtMid(head);
    Node* sortedLeft = mergeSort(head);
    Node* sortedRight =mergeSort(rightHead);

    return merge(sortedLeft, sortedRight);
}

Node* reverse(Node* head) {
    Node* prev = NULL;
    Node* curr = head;

    while(curr != NULL) {
        Node* next = curr->next;

        curr->next = prev;
        prev = curr;
        curr = next;
    }

    return prev; // prev is head
}

void printList(Node* head) {
    Node* temp = head;

    while(temp != NULL) {
        cout << temp->data << " ";
        temp = temp->next;
    }
    cout << endl;
}

Node* zigzag(Node* head) {
    Node* rightHead = splitAtMid(head);
    Node* rightRev = reverse(rightHead);

    //alternate merging
    Node* left = head;
    Node* right = rightRev;
    Node* nextLeft = NULL;
    Node* nextRight = NULL;
    Node* tail = head;

    while(left != NULL && right != NULL) {
        nextLeft = left->next;
        left->next = right;

        nextRight = right->next;
        right->next = nextLeft;

        tail = right;
        left = nextLeft;
        right = nextRight;
    }

    if(right != NULL) {
        tail->next = right;
    }
    return head;
}

int main(){
       List ll;

       //QS : Cycle Detection & Removal
       /* ll.push_front(4);
       ll.push_front(3);
       ll.push_front(2);
       ll.push_front(1);

       ll.tail->next = ll.head; //creating a cycle

        cout << isCycle(ll.head) << endl;
        removeCycle(ll.head);
        cout << isCycle(ll.head) << endl;
        ll.printList(); */

        //QS : Merge Sort the Linked List
        // ll.push_front(1);
        // ll.push_front(2);
        // ll.push_front(3);
        // ll.push_front(4);
        // ll.printList();

        // ll.head = mergeSort(ll.head);
        // ll.printList();

        //QS : Zig Zag Linked List
        ll.push_front(5);
        ll.push_front(4);
        ll.push_front(3);
        ll.push_front(2);
        ll.push_front(1);
        ll.printList();

        ll.head = zigzag(ll.head);
        ll.printList();
}


================================================
FILE: 26_LinkedList2/list_using_stl.cpp
================================================
#include <iostream>
#include <list>
#include <iterator>
using namespace std;

void printList(list<int> ll) {
    list<int>::iterator itr;
    for(itr=ll.begin(); itr!=ll.end(); itr++) {
        cout << *itr << " ";
    }
    cout << endl;
}

int main() {
    list<int> ll;

    ll.push_front(2);
    ll.push_front(1);

    ll.push_back(3);
    ll.push_back(4);

    cout << "size : " << ll.size() << endl;

    printList(ll);
    
    cout << "head = " << ll.front() << endl;
    cout << "tail = " << ll.back() << endl;

    ll.pop_front();
    ll.pop_back();

    printList(ll);
    return 0;
}

================================================
FILE: README.md
================================================
# Cpp-DSAClasses
This repo contains the codes of C++ DSA Batch of Apna College.