In this tutorial I will explain about algorithm for insertion sort in C and C++ using program example. The insertion sort inserts each element in proper place. The strategy behind the insertion sort is similar to the process of sorting a pack of cards. You can take a card, move it to its location in sequence and move the remaining cards left or right as needed.
In insertion sort, we assume that first element A[0] in pass 1 is already sorted. In pass 2 the next second element A[1] is compared with the first one and inserted into its proper place either before or after the first element. In pass 3 the third element A[2] is inserted into its proper place and so on.
Algorithm for Insertion Sort in C & C++
Let ARR is an array with N elements
1. Read ARR
2. Repeat step 3 to 8 for I=1 to N-1
3. Set Temp=ARR[I]
4. Set J=I-1
5. Repeat step 6 and 7 while Temp<ARR[J] AND J>=0
6. Set ARR[J+1]=ARR[J] [Moves element forward]
7. Set J=J-1
[End of step 5 inner
loop]
loop]
8. Set ARR[J+1]=Temp [Insert element in proper place]
[End of step 2 outer
loop]
loop]
9. Exit
Program for Insertion Sort in C
#include<stdio.h>
int main()
{
int i,j,n,temp,a[30];
printf("Enter the number of elements:");
scanf("%d",&n);
printf("\nEnter the elements\n");
for(i=0;i<n;i++)
{
scanf("%d",&a[i]);
}
for(i=1;i<=n-1;i++)
{
temp=a[i];
j=i-1;
while((temp<a[j])&&(j>=0))
{
a[j+1]=a[j]; //moves element forward
j=j-1;
}
a[j+1]=temp; //insert element in proper place
}
printf("\nSorted list is as follows\n");
for(i=0;i<n;i++)
{
printf("%d ",a[i]);
}
return 0;
}
Program for Insertion Sort in C++
#include<iostream>
using namespace std;
int main()
{
int i,j,n,temp,a[30];
cout<<"Enter the number of elements:";
cin>>n;
cout<<"\nEnter the elements\n";
for(i=0;i<n;i++)
{
cin>>a[i];
}
for(i=1;i<=n-1;i++)
{
temp=a[i];
j=i-1;
while((temp<a[j])&&(j>=0))
{
a[j+1]=a[j]; //moves element forward
j=j-1;
}
a[j+1]=temp; //insert element in proper place
}
cout<<"\nSorted list is as follows\n";
for(i=0;i<n;i++)
{
cout<<a[i]<<" ";
}
return 0;
}
Complexity of Insertion Sort in C & C++
There is 1 comparison during pass 1 for proper place. There are 2 comparisons during pass 2 for proper place. There are 3 comparisons during pass 3 for proper place, and so on accordingly.
F(n) = 1 + 2 + 3 + . . . . + (n-1) = n (n-1)/2 = O(n2)
Hence complexity for insertion sort program in C and C++ is O(n2).
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