Example: Merge Sort Algorithm in C++

// Merge Sort Algorithm
#include <iostream>
#include <vector> // Using vector for dynamic arrays and ease of use

// Function to merge two halves of an array
void merge(std::vector<int>& arr, int left, int mid, int right) {
    int n1 = mid - left + 1;
    int n2 = right - mid;

    // Create temporary vectors
    std::vector<int> L(n1);
    std::vector<int> R(n2);

    // Copy data to temporary vectors 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 vectors back into arr[left..right]
    int i = 0; // Initial index of first sub-vector
    int j = 0; // Initial index of second sub-vector
    int k = left; // Initial index of merged array

    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++;
    }
}

// Function to implement Merge Sort
void mergeSort(std::vector<int>& arr, int left, int right) {
    if (left >= right) { // Base case: if array has 0 or 1 element
        return;
    }
    int mid = left + (right - left) / 2;
    mergeSort(arr, left, mid); // Sort first half
    mergeSort(arr, mid + 1, right); // Sort second half
    merge(arr, left, mid, right); // Merge the sorted halves
}

// Helper function to print the array
void printArray(const std::vector<int>& arr) {
    for (int i = 0; i < arr.size(); i++) {
        std::cout << arr[i] << " ";
    }
    std::cout << std::endl;
}

int main() {
    // Step 1: Initialize an unsorted vector
    std::vector<int> arr = {38, 27, 43, 3, 9, 82, 10};
    std::cout << "Original array: ";
    printArray(arr);

    // Step 2: Apply Merge Sort
    mergeSort(arr, 0, arr.size() - 1);

    // Step 3: Print the sorted array
    std::cout << "Sorted array: ";
    printArray(arr);

    return 0;
}