C Program for Merge Sort

C program for merge sort: The following C program uses merge sort algorithm to accept and sort an array in ascending as well as descending order.

C program for merge sort

#include<stdlib.h>
#include<stdio.h>
 
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++;
    }
}
 
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);
    }
}
 
void displayArray(int Arr[], int size)
{
    int i;

    for (i=0; i < size; i++)
        printf("%d ", Arr[i]);

    printf("\n");
}

int main()
{
 int Arr_size;

 print("\n Enter array size:- ");
 scanf("%d",&size);

 printf("Given array is \n");
    displayArray(arr, Arr_size);
 
    mergeSort(arr, 0, Arr_size - 1);
 
    printf("\n Sorted array is: ");
    displayArray(arr, Arr_size);

    return 0;
}

Get This Program:   The time complexity of merge sort algorithm is O(nlog_n). The divide step computes the midpoint of each of the sub-arrays. Each of this step just It just requires O(1) time to divide and computer midpoint of each of the sub arrays. Then the conquer step sorts two subarrays of n/2 (for even n) elements each recursively.

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