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How to swap two bits in a given integer?

Given an integer n and two bit positions p1 and p2 inside it, swap bits at the given positions. The given positions are from least significant bit (lsb). For example, the position for lsb is 0.

Examples:

Input: n = 28, p1 = 0, p2 = 3
Output: 21
28 in binary is 11100.  If we swap 0'th and 3rd digits, 
we get 10101 which is 21 in decimal.

Input: n = 20, p1 = 2, p2 = 3
Output: 24

We strongly recommend you to minimize your browser and try this yourself first.

The idea is to first find the bits, then use XOR based swapping concept, i..e., to swap two numbers ‘x’ and ‘y’, we do x = x ^ y,  y = y ^ x and x = x ^ y.

Below is the implementation of the above idea

C++

// C program to swap bits in an intger
#include<stdio.h>
  
// This function swaps bit at positions p1 and p2 in an integer n
int swapBits(unsigned int n, unsigned int p1, unsigned int p2)
{
    /* Move p1'th to rightmost side */
    unsigned int bit1 =  (n >> p1) & 1;
  
    /* Move p2'th to rightmost side */
    unsigned int bit2 =  (n >> p2) & 1;
  
    /* XOR the two bits */
    unsigned int x = (bit1 ^ bit2);
  
    /* Put the xor bit back to their original positions */
    x = (x << p1) | (x << p2);
  
    /* XOR 'x' with the original number so that the
       two sets are swapped */
    unsigned int result = n ^ x;
}
  
/* Drier program to test above function*/
int main()
{
    int res =  swapBits(28, 0, 3);
    printf("Result = %d ", res);
    return 0;
}

Java

// Java program to swap bits in an intger
import java.io.*;
  
class GFG 
{
      
// This function swaps bit at 
// positions p1 and p2 in an integer n
static int swapBits( int n, int p1, int p2)
{
    /* Move p1'th to rightmost side */
    int bit1 = (n >> p1) & 1;
  
    /* Move p2'th to rightmost side */
    int bit2 = (n >> p2) & 1;
  
    /* XOR the two bits */
    int x = (bit1 ^ bit2);
  
    /* Put the xor bit back to
    their original positions */
    x = (x << p1) | (x << p2);
  
    /* XOR 'x' with the original
    number so that the
    two sets are swapped */
    int result = n ^ x;
    return result;
}
  
    /* Driver code*/
    public static void main (String[] args)
    {
        int res = swapBits(28, 0, 3);
        System.out.println ("Result = " + res);
    }
}
  
// This code is contributed by ajit..

/div>

C#

// C# program to swap bits in an intger
using System;
  
class GFG
{
          
// This function swaps bit at positions 
// p1 and p2 in an integer n
static int swapBits(int n, int p1, int p2)
{
    /* Move p1'th to rightmost side */
    int bit1 = (n >> p1) & 1;
  
    /* Move p2'th to rightmost side */
    int bit2 = (n >> p2) & 1;
  
    /* XOR the two bits */
    int x = (bit1 ^ bit2);
  
    /* Put the xor bit back to
    their original positions */
    x = (x << p1) | (x << p2);
  
    /* XOR 'x' with the original
    number so that the
    two sets are swapped */
    int result = n ^ x;
    return result;
}
  
/* Driver code*/
static public void Main ()
{
    int res = swapBits(28, 0, 3);
    Console.WriteLine("Result = " + res);
}
}
  
// This code is contributed by akt_mit


Output:

Result = 21

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above



This article is attributed to GeeksforGeeks.org

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