Merge_sort.cpp

 #include <iostream>
 using namespace std;

 void merge(int a[], int l, int m, int r) {
     int n1 = m - l + 1, n2 = r - m;
     int L[n1], R[n2];
     for (int i = 0; i < n1; i++) L[i] = a[l + i];
     for (int j = 0; j < n2; j++) R[j] = a[m + 1 + j];
     int i = 0, j = 0, k = l;
     while (i < n1 && j < n2) a[k++] = (L[i] <= R[j]) ? L[i++] : R[j++];
     while (i < n1) a[k++] = L[i++];
     while (j < n2) a[k++] = R[j++];
 }
 void mergeSort(int a[], int l, int r) {
     if (l < r) {
         int m = l + (r - l) / 2;
         mergeSort(a, l, m);
         mergeSort(a, m + 1, r);
         merge(a, l, m, r);
     }
 }
 int main() {
     int a[] = {12, 11, 13, 5, 6, 7};
     int n = 6;
     mergeSort(a, 0, n - 1);
     for (int i = 0; i < n; i++) cout << a[i] << " ";
 }