C++ Program For Merge Sort

// C++ program for the implementation of merge sort
#include <iostream>
#include <vector>

using namespace std;

// Merges two subarrays of vec.
// First subarray is vec[left..mid]
// Second subarray is vec[mid+1..right]
void merge(vector<int>& vec, int left, int mid, int right) {
    int i, j, k;
    int n1 = mid - left + 1;
    int n2 = right - mid;

    // Create temporary vectors
    vector<int> leftVec(n1), rightVec(n2);

    // Copy data to temporary vectors
    for (i = 0; i < n1; i++)
        leftVec[i] = vec[left + i];
    for (j = 0; j < n2; j++)
        rightVec[j] = vec[mid + 1 + j];

    // Merge the temporary vectors back into vec[left..right]
    i = 0;
    j = 0;
    k = left;
    while (i < n1 && j < n2) {
        if (leftVec[i] <= rightVec[j]) {
            vec[k] = leftVec[i];
            i++;
        } else {
            vec[k] = rightVec[j];
            j++;
        }
        k++;
    }

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

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

// The subarray to be sorted is in the index range [left..right]
void mergeSort(vector<int>& vec, int left, int right) {
    if (left < right) {
      
        // Calculate the midpoint
        int mid = left + (right - left) / 2;

        // Sort first and second halves
        mergeSort(vec, left, mid);
        mergeSort(vec, mid + 1, right);

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

int main() {
    vector<int> vec = {12, 11, 13, 5, 6, 7};
    int n = vec.size();

    // Sorting vec using mergesort
    mergeSort(vec, 0, n - 1);

    for (auto i: vec)
        cout << i << " ";
    return 0;
}