merge sort.cpp

#include <iostream>
using namespace std;

// Function to merge two halves into a sorted array
void merge(int arr[], int left, int mid, int right) {
    int n1 = mid - left + 1;  // Size of the left subarray
    int n2 = right - mid;     // Size of the right subarray

    int leftArray[n1], rightArray[n2];

    // Copy data to temporary arrays
    for (int i = 0; i < n1; i++)
        leftArray[i] = arr[left + i];
    for (int j = 0; j < n2; j++)
        rightArray[j] = arr[mid + 1 + j];

    // Merging the arrays
    int i = 0, j = 0, k = left;
    while (i < n1 && j < n2) {
        if (leftArray[i] <= rightArray[j]) {
            arr[k] = leftArray[i];
            i++;
        } else {
            arr[k] = rightArray[j];
            j++;
        }
        k++;
    }

    // Copy remaining elements of leftArray[], if any
    while (i < n1) {
        arr[k] = leftArray[i];
        i++;
        k++;
    }

    // Copy remaining elements of rightArray[], if any
    while (j < n2) {
        arr[k] = rightArray[j];
        j++;
        k++;
    }
}

// Function to implement Merge Sort
void mergeSort(int arr[], int left, int right) {
    if (left < right) {
        int mid = left + (right - left) / 2;  // Calculate the midpoint to split the array

        // Recursively sort the first and second halves
        mergeSort(arr, left, mid);
        mergeSort(arr, mid + 1, right);

        // Merge the sorted halves
        merge(arr, left, mid, right);
    }
}

int main() {
    int arr[] = {12, 11, 13, 5, 6, 7};
    int arrSize = sizeof(arr) / sizeof(arr[0]);

    cout << "Given array: ";
    for (int i = 0; i < arrSize; i++)
        cout << arr[i] << " ";
    cout << endl;

    mergeSort(arr, 0, arrSize - 1);

    cout << "Sorted array: ";
    for (int i = 0; i < arrSize; i++)
        cout << arr[i] << " ";
    cout << endl;

    return 0;
}