Example: Merge Sort Implementation in C++

// Merge Sort Implementation
#include <iostream>
#include <vector> // Using vector for dynamic array in main, but merge sort works with raw arrays too.

// Function to merge two sorted subarrays
void merge(int arr[], int left, int mid, int right) {
    int n1 = mid - left + 1;
    int n2 = right - mid;

    // Create temporary arrays
    int* L = new int[n1];
    int* R = new int[n2];

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

    // Merge the temporary arrays back into arr[left..right]
    int i = 0; // Initial index of first subarray
    int j = 0; // Initial index of second subarray
    int k = left; // Initial index of merged subarray

    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) {
            arr[k] = L[i];
            i++;
        } else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

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

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

    // Free the dynamically allocated memory
    delete[] L;
    delete[] R;
}

// Placeholder for main function to demonstrate calling merge conceptually
// int main() {
//     int arr[] = {3, 5, 2, 4}; // Example: merge([3,5], 0, 0, 1) and ([2,4], 2, 2, 3)
//     // After sorting subarrays: [3,5] and [2,4]
//     // Call merge(arr, 0, 1, 3) where arr currently is {3,5,2,4}
//     // Expected output of merge would transform arr to {2,3,4,5}
//     return 0;
// }