MergeSort.cpp

#include <stdio.h>

void merge(int arr[], int left, int mid, int right)
{
    int i, j, k;

    int n1 = mid - left + 1;
    int n2 = right - mid;

    int L[n1], R[n2];

    for (i = 0; i < n1; i++)
        L[i] = arr[left + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[mid + 1 + j];

    i = 0;
    j = 0;
    k = left;
    while (i < n1 && j < n2)
    {
        if (L[i] <= R[j])
            arr[k++] = L[i++];
        else
            arr[k++] = R[j++];
    }

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

void mergeSort(int arr[], int left, int right)
{
    if (left < right)
    {
        int mid = (left + right) / 2;

        // Sort 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 n = sizeof(arr) / sizeof(arr[0]);

    mergeSort(arr, 0, n - 1);

    return 0;
}