merge_sort.cpp

#include<iostream>
using namespace std;
void merge(int *array, int l, int m, int r) {
   int i, j, k, nl, nr;
   nl = m-l+1; nr = r-m;
   int larr[nl], rarr[nr];
   for(i = 0; i<nl; i++)
      larr[i] = array[l+i];
   for(j = 0; j<nr; j++)
      rarr[j] = array[m+1+j];
   i = 0; j = 0; k = l;
   while(i < nl && j<nr) {
      if(larr[i] <= rarr[j]) {
         array[k] = larr[i];
         i++;
      }else{
         array[k] = rarr[j];
         j++;
      }
      k++;
   }
   while(i<nl) {       //extra element in left array
      array[k] = larr[i];
      i++; k++;
   }
   while(j<nr) {     //extra element in right array
      array[k] = rarr[j];
      j++; k++;
   }
}
void mergeSort(int *array, int l, int r) {
   int m;
   if(l < r) {
      int m = l+(r-l)/2;
      // Sort first and second arrays
      mergeSort(array, l, m);
      mergeSort(array, m+1, r);
      merge(array, l, m, r);
   }
}
int main() {
   int n;
   cout << "Enter the number of elements: ";
   cin >> n;
   int arr[n];     //create an array with given number of elements
   cout << "Enter elements:" << endl;
   for(int i = 0; i<n; i++) {
      cin >> arr[i];
   }
   cout << "Array before Sorting: ";
   for(int i=0;i<n;i++){
           cout<<arr[i]<<" ";
   }
   cout<<endl;
   mergeSort(arr, 0, n-1);     //(n-1) for last index
   cout << "Array after Sorting: ";
   for(int i=0;i<n;i++){
           cout<<arr[i]<<" ";
   }
   cout<<endl;
}