Mergesort.c

//By Aadhaar koul
//Cse - A1 - 2020a1r040
//Mergesort in c language
//Comments have been Implemented for better understanding
//( Authentic Code ) - No plagiarism Done
//*All rights Reserved with the owner

#include <stdio.h>
 
// function to sort the subsection a[i .. j] of the array a[]
void merge_sort(int i, int j, int a[], int aux[]) {
    if (j <= i) {
        return;     

        // the subsection is empty or a single element
    }
    int mid = (i + j) / 2;

    // left sub-array is a[i .. mid]
    // right sub-array is a[mid + 1 .. j]
    
    merge_sort(i, mid, a, aux);    

     // sort the left sub-array recursively
    
    merge_sort(mid + 1, j, a, aux);     

    // sort the right sub-array recursively

    int pointer_left = i;       

    // pointer_left points to the beginning of the left sub-array
    
    int pointer_right = mid + 1;        

    // pointer_right points to the beginning of the right sub-array
    
    int k;      

    // k is the loop counter

    // we loop from i to j to fill each element of the final merged array
    for (k = i; k <= j; k++) {
        if (pointer_left == mid + 1) {      

        // left pointer has reached the limit
        
            aux[k] = a[pointer_right];
            pointer_right++;
        } else if (pointer_right == j + 1) {        

        // right pointer has reached the limit
        
            aux[k] = a[pointer_left];
            pointer_left++;
        } else if (a[pointer_left] < a[pointer_right]) {       

         // pointer left points to smaller element
        
            aux[k] = a[pointer_left];
            pointer_left++;
        } else {        

        // pointer right points to smaller element
        
            aux[k] = a[pointer_right];
            pointer_right++;
        }
    }

    for (k = i; k <= j; k++) {      

    // copy the elements from aux[] to a[]

        a[k] = aux[k];
    }
}


int main() {

    //Declaring the arrays and Integers

  int a[100], aux[100], n, i, d, swap;

  //Taking inputs of the Number of elements
 
  printf("Enter number of elements you want to sort.\n");
  scanf("%d", &n);
 
  //Storing the Elements

  printf("Enter the elements\n");
 
  for (i = 0; i < n; i++)
    scanf("%d", &a[i]);


  printf("Unsorted array :\n");
  for (i = 0; i < n; ++i)
  {
      printf("| %d |", a[i]);
  }

  printf("\n");

  //Calling the mergesort function
 
  merge_sort(0, n - 1, a, aux);

  //Printing the sorted arrayy
 
  printf("\nSorted array:\n");
 
  for (int i = 0; i < n; i++)
     printf("| %d |", a[i]);
 
  return 0;

  //End
}