mergesort.c

#include <stdio.h>
#include <stdlib.h>
 
void merge(int arr[], int left, int mid, int right)
{
    int i, j, k;
    int size1 = mid - left + 1;
    int size2 = right - mid;
 
    // created temporary array
    int Left[size1], Right[size2];
 
    // copying the data from arr to temporary array
    for (i = 0; i < size1; i++)
        Left[i] = arr[left + i];
 
    for (j = 0; j < size2; j++)
        Right[j] = arr[mid + 1 + j];
 
    // merging of the array
    i = 0;	// intital index of first subarray
    j = 0;	// inital index of second subarray
    k = left; // initial index of parent array
    while (i < size1 && j < size2)
    {
        if (Left[i] <= Right[j])
        {
            arr[k] = Left[i];
            i++;
        }
        else
        {
            arr[k] = Right[j];
            j++;
        }
        k++;
    }
 
    // copying the elements from Left[], if any
    while (i < size1)
    {
        arr[k] = Left[i];
        i++;
        k++;
    }
 
    // copying the elements from Right[], if any
    while (j < size2)
    {
        arr[k] = Right[j];
        j++;
        k++;
    }
}
 
//merge sort function
void mergesort(int arr[], int left, int right)
{
    if (left < right)
    {
 
        int mid = left + (right - left) / 2;
 
        // recursive calling of merge_sort
        mergesort(arr, left, mid);
        mergesort(arr, mid + 1, right);
 
        merge(arr, left, mid, right);
    }
}
 
// driver code
int main()
{
    int size;
    printf("Enter the size: ");
    scanf("%d", &size);
 
    int arr[size];
    
    for (int i = 0; i < size; i++)
    {printf("Enter arr[%d]: ",i);
        scanf("%d", &arr[i]);
    }

    printf("Unsorted Array: ");
    for (int i = 0; i < size; i++)
    {
        printf("%d ", arr[i]);
    }
    printf("\n");

    mergesort(arr, 0, size - 1);
 
    printf("Sorted Array: ");
    for (int i = 0; i < size; i++)
    {
        printf("%d ", arr[i]);
    }
    printf("\n");
    return 0;
}