Merge Sort algorithm

Merge Sort algorithm in C++ language

This particular algorithm also depends 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:

//header files for program implementation

#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