Insertion Sort


Sorting is the process of arranging a list of elements in a particular order (Ascending or Descending).

Insertion sort algorithm arranges a list of elements in a particular order. In insertion sort algorithm, every iteration moves an element from unsorted portion to sorted portion until all the elements are sorted in the list.

Step by Step Process

The insertion sort algorithm is performed using following steps...

  • Step 1: Asume that first element in the list is in sorted portion of the list and remaining all elements are in unsorted portion.
  • Step 2: Consider first element from the unsorted list and insert that element into the sorted list in order specified.
  • Step 3: Repeat the above process until all the elements from the unsorted list are moved into the sorted list.

Sorting Logic

Following is the sample code for insrtion sort...

     
   //Insertion sort logic
   for i = 1 to size-1 {
      temp = list[i];
      j = i;
      while ((temp < list[j]) && (j > 0)) {
         list[j] = list[j-1];
         j = j - 1;
      }
      list[j] = temp;
   }
 

Example

Complexity of the Insertion Sort Algorithm

To sort a unsorted list with 'n' number of elements we need to make (1+2+3+......+n-1) = (n (n-1))/2 number of comparisions in the worst case. If the list already sorted, then it requires 'n' number of comparisions.

Worst Case : O(n2)
Best Case : Ω(n)
Average Case : Θ(n2)

Insertion Sort Program in C Programming Language

#include<stdio.h>
#include<conio.h>

void main(){

   int size, i, j, temp, list[100];
 
   printf("Enter the size of the list: ");
   scanf("%d", &size);
 
   printf("Enter %d integer values: ", size);
   for (i = 0; i < size; i++) 
      scanf("%d", &list[i]);
      
   //Insertion sort logic
   for (i = 1; i < size; i++) {
      temp = list[i];
      j = i - 1;
      while ((temp < list[j]) && (j >= 0)) {
         list[j + 1] = list[j];
         j = j - 1;
      }
      list[j + 1] = temp;
   }
 
   printf("List after Sorting is: ");
   for (i = 0; i < size; i++)
      printf(" %d", list[i]);

  getch();
}