# Merge Sort algorithm

Implementation of Merge Sort algorithm in C++ language

This particular algorithm is also depend upon the divide and conquer technique.Its design paradigm is based on multi-branched recursion. It works by recursively breaking down a problem into two or more sub-problems of the same or related type, until these become simple enough to be solved directly.

Program Code:
#include<iostream>
using namespace std;

// function definition which is going to merge or combine the solved sub-problem

void merge(int arr[], int l, int m, int r)
{
int i, j, k;
int n1 = m - l + 1;
int n2 =  r - m;
int L[n1], R[n2];
for (i = 0; i < n1; i++)
L[i] = arr[l + i];
for (j = 0; j < n2; j++)
R[j] = arr[m + 1+ j];
i = 0;
j = 0;
k = l;
while (i < n1 && j < n2)
{
if (L[i] <= R[j])
{
arr[k] = L[i];
i++;
}
else
{
arr[k] = R[j];
j++;
}
k++;
}
while (i < n1)
{
arr[k] = L[i];
i++;
k++;
}
while (j < n2)
{
arr[k] = R[j];
j++;
k++;
}
}

// this function is divide the problem into sub-problems equally recursively

void mergeSort(int arr[], int l, int r)
{
if (l < r)
{
int m = l+(r-l)/2;
mergeSort(arr, l, m);
mergeSort(arr, m+1, r);
merge(arr, l, m, r);
}
}

// this function display the array elements

void printArray(int A[], int size)
{
int i;
for (i=0; i < size; i++)
cout<< A[i]<<"\t";
cout<<endl;
}

// main() function with different function calls

int main()
{
int arr[] = {12, 11, 13, 5, 6, 7, 2, 3, 8, 9, 18, 20};
int arr_size = sizeof(arr)/sizeof(arr[0]);
cout<<"The given array for sorting is :"<<endl;
printArray(arr, arr_size);
mergeSort(arr, 0, arr_size - 1);
cout<<"After applying merge sort the above array is:"<<endl;
printArray(arr, arr_size);
return 0;
}

The program output is tested on www.jdoodle.com
Output:
The given array for sorting is :
12 11 13 5 6 7 2 3 8 9 18 20
After applying merge sort the above array is:
2 3 5 6 7 8 9 11 12 13 18 20

Thanks
Mukesh Rajput

Mukesh Rajput

I am a Computer Engineer, a small amount of the programming tips as it’s my hobby, I love to travel and meet people so little about travel, a fashion lover and love to eat food, I am investing a good time to keep the body fit so little about fitness also..