Merge Sort in C++

 A simple program to demonstrate merge sort algorithm in C++ programming language.

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Program Listing
merge.cpp
#include <iostream>
#include <vector>

// Merge two sorted arrays into one sorted array
void merge(std::vector<int>& arr, int left, int mid, int right) {
    int n1 = mid - left + 1;
    int n2 = right - mid;

    std::vector<int> L(n1);
    std::vector<int> R(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];

    int i = 0, j = 0, k = left;

    // Merge the temporary arrays back into arr
    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 and R (if any)
    while (i < n1) {
        arr[k] = L[i];
        ++i;
        ++k;
    }

    while (j < n2) {
        arr[k] = R[j];
        ++j;
        ++k;
    }
}

// Merge Sort function
void mergeSort(std::vector<int>& arr, int left, int right) {
    if (left < right) {
        int mid = left + (right - left) / 2;

        // 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() {
    std::vector <int> arr = {12, 11, 13,-67,23,-452, 5, 6, 7};


    std::cout << "\n\t\tMerge Sort in C++\n\n";
    std::cout << "\n\tOriginal array: ";
    for (int num : arr)
        std::cout << num << " ";

    mergeSort(arr, 0, arr.size() - 1);

    std::cout << "\n\n\tSorted array: ";
    for (int num : arr)
        std::cout << num << " ";
    std::cout <<"\n\n";
    return 0;
}