Array Rotation using Reversal Algorithm

Array Rotation Using Revesal Algorithm :

Given an array of N size. The task is to rotate array by d elements where d is less than or equal to N.

Sample Input:

n=7

arr[]={1,2,3,4,5,6,7}

d=2

Output:

3,4,5,6,7,1,2

Algorithm:

step1 : Reverse the elements starting from index 0 to d-1.

step2 : Reverse the elements from index d to n-1.

step3 : Reverse the entire array

For the given sample input,

After step 1:

   arr[]={2,1,3,4,5,6,7}

After step 2:

   arr[]={2,1,7,6,5,4,3}

After step 3:

   arr[]={3,4,5,6,7,1,2}

Program:

 

#include <stdio.h>

void reverse(int a[],int start,int end)
{      

      int temp;

      while(start<end)

       {

            temp=a[start];

            a[start]=a[end];

            a[end]=temp;

            start++;

            end--;

        }

}
void RotateArray(int a[],int n,int d)
{
         reverse(a,0,d-1);
         reverse(a,d,n-1);
         reverse(a,0,n-1);
}

void printArray(int a[],int n)
{
     int i;
         for(i=0;i<n;i++)

     printf("%d ",a[i]);
     printf("\n");
}

int main() 

{
        int n,i,d;

        scanf("%d",&n);
        int a[n];
        for(i=0;i<n;i++)

             scanf("%d",&a[i]);

        scanf("%d",&d);
        RotateArray(a,n,d);
        printArray(a,n);
        return 0;
}