Swap_even_odd_bits.java

/* This program will swap even and odd bits of
the given integer.
For Ex: 
        If the given number is 21(00010101) the ouput 
        should be 42(00101010).
*/
import java.util.*;
import java.lang.*;
import java.io.*;

class swap_even_odd_bits
{
	public static void main (String[] args) throws java.lang.Exception
	{
		
       Scanner scn = new Scanner(System.in);
        System.out.println("Enter the number:");
        int n=scn.nextInt();

       //e represents hexadecimal number 1010(10)
        int e=0xAAAAAAAA ;

       //o represents hexadecimal number 0101(5)
        int o=0x55555555;

       //this will preserve all even bits of n and
       //make all odd bits of n 0.
        int even= e&n;

        //this will preserve all odd bits of n and
       //make all even bits of n 0.
        int odd= o&n;

        even >>= 1;
        odd <<= 1;
        
        System.out.println(even | odd); 
	}
}

/*           TEST CASES

   1)Input:
           Enter the number:
           25
    Output:
           38
   
   2)Input:
           Enter the number:
           32
    Output:
           16
           

    Time Complexity:  O(1)
    Space Complexity: O(1)
*/