C program of Merge Sort Algorithm

C program of Merge sort algorithm : Merge sort is based on the divide-and-conquer paradigm. Its worst-case running time has a lower order of growth than insertion sort. Since we are dealing with sub problems, we state each sub problem as sorting a sub array A[p .. r]. Initially, p = 1 and r = n, but these values change as we recursive through sub problems.

To sort A[p .. r]:

1. Divide Step

If a given array A has zero or one element, simply return; it is already sorted. Otherwise, split A[p .. r] into two subarrays A[p .. q] and A[q + 1 .. r], each containing about half of the elements of A[p .. r]. That is, q is the halfway point of A[p .. r].

2. Conquer Step

Conquer by recursively sorting the two subarrays A[p .. q] and A[q + 1 .. r].

3. Combine Step

Combine the elements back in A[p .. r] by merging the two sorted subarrays A[p .. q] and A[q + 1 .. r] into a sorted sequence. To accomplish this step, we will define a procedure MERGE (Apqr).

Note that the recursion bottoms out when the sub array has just one element, so that it is trivially sorted.

C program of Merge Sort Algorithm

Algorithm: Merge Sort

To sort the entire sequence A[1 .. n], make the initial call  to the procedure MERGE-SORT (A, 1, n).

Merge Sort
 
MERGE-SORT (A, p, r)
 
1.     IF p < r                                                    // Check for base case
2.         THEN q = FLOOR[(p + r)/2]                 // Divide step
3.                 MERGE (A, p, q)                          // Conquer step.
4.                 MERGE (A, q + 1, r)                     // Conquer step.
5.                 MERGE (A, p, q, r)                       // Conquer step.

C program of Merge Sort Algorithm :

C program of Merge Sort Algorithm
 
#include<stdio.h>
#include<conio.h>
int a[50];
void merge(int,int,int);
void merge_sort(int low,int high)
{
 int mid;
 if(low<high)
 {
  mid=(low+high)/2;
  merge_sort(low,mid);
  merge_sort(mid+1,high);
  merge(low,mid,high);
 }
}
void merge(int low,int mid,int high)
{
 int h,i,j,b[50],k;
 h=low;
 i=low;
 j=mid+1;
 while((h<=mid)&&(j<=high))
 {
  if(a[h]<=a[j])
  {
   b[i]=a[h];
   h++;
  }
  else
  {
   b[i]=a[j];
   j++;
  }
  i++;
 }
 if(h>mid)
 {
  for(k=j;k<=high;k++)
  {
   b[i]=a[k];
   i++;
  }
 }
 else
 {
  for(k=h;k<=mid;k++)
  {
   b[i]=a[k];
   i++;
  }
 }
 for(k=low;k<=high;k++) a[k]=b[k];
}
int main()
{
 int num,i;
 printf("------------------------------------------------------------------\n");
 printf("---------------------- Made by C code champ ----------------------\n");
 printf("------------------------------------------------------------------\n\n");
 printf("\t\t\tMERGE SORT\n");
 printf("\nEnter the total numbers: ");
 scanf("%d",&num);
 printf("\nEnter %d numbers: \n",num);
 for(i=1;i<=num;i++)
 {
  scanf("%d",&a[i]);
 }
 merge_sort(1,num);
 printf("\nSORTED ORDER: \n");
 for(i=1;i<=num;i++) printf("\t%d",a[i]);
 getch();
}

 

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