merge sort.cpp

#include<bits/stdc++.h>
typedef long long ll;
#define endl "\n"
using namespace std;


void merge(int arr[]   , int  l , int mid   , int  r){

  int n1= mid - l + 1  ; 
  int n2 = r- mid;
  int a[n1] , b[n2];
  for(int i =0 ;i<n1;i++)
     a[i] = arr[l+i];

  for(int i =0 ;i<n1;i++)
     b[i] =arr[mid+1+i];

  int i=0,j=0,k=l;

  while(i<n1  &&  j<n2){
  if(a[i]<b[j]){
       arr[k] =a[i];
       i++;k++;
  }
  else{
         arr[k] =b[j];
       j++;k++;
  }

  }

  while(i<n1){ 
      arr[k] =a[i];
       i++;k++;
  }
  while( j<n2){   arr[k] =b[j];
       j++;k++;
  }
}




void  mergeSort(int arr[], int l , int r){

if(l<r){

  int mid = (l+r) / 2;
  mergeSort(arr , l , mid);
  mergeSort(arr , mid+1 , r);
  merge(arr,l,mid, r);
}

}

int main()
{
    //system("CLS");
    int arr[]={88,38,9,5,2,8,7,1};
    mergeSort(arr,0,7);
    for(int i=0;i<8;i++)
    {
        cout<<arr[i]<<" ";
    }
        return 0;
}