mergesort.cpp

/* MERGE SORT */

#include <iostream>
#include <vector>
using namespace std;

void mergepass (vector<int> &a, int low, int mid, int high)
{
        vector<int> b(20);
        int h = low, i = low, j = mid+1, k;
        while((h<=mid) && (j<=high)){
          if(a[h] < a[j]){
            b[i++] = a[h++];
          }
          else{
            b[i++] = a[j++];
          }
        }
        if(h>mid){
          for(k = j; k<=high; k++){
            b[i] = a[k];
            i++;
          }
        }
        else{
          for(k=h; k<=mid; k++){
           b[i] = a[k];
           i++;
          }
        }
        for( k=low; k<=high; k++)
          a[k] = b[k];
}
void mergesort(vector<int> &a, int low, int high)
{
        if(low != high){
        int  mid= (low+high)/2;
        mergesort(a,low, mid);
        mergesort(a, mid+1, high);
        mergepass(a, low, mid, high);
        }
}

main()
{
        vector<int> v(20);
        int n, low, high;
        cout<<"enter number of elements";
        cin>> n;
        cout<<"enter values"<<endl;
        for(int i=1; i<=n; i++){
         cout<<i<<": ";
         cin>>v[i];
        }
        low = 1; high = n;
        mergesort(v, low, high);
        for (int j=1; j<=n; j++)
          cout<<v[j]<<" ";
}