# Swap all odd and even bits

• Difficulty Level : Medium
• Last Updated : 14 Feb, 2022

Given an unsigned integer, swap all odd bits with even bits. For example, if the given number is 23 (00010111), it should be converted to 43 (00101011). Every even position bit is swapped with adjacent bit on right side (even position bits are highlighted in binary representation of 23), and every odd position bit is swapped with adjacent on left side.

It is very hard to remember  0xAAAAAAAA as a number of 32 bit which is set at all even bits and 0x55555555  as a number of 32 bit which is set at all odd bits. So there is another solution for this. Here we need to perform operation in a brute force manner.

1. Find bit of and i+1.
2. To swap the bits subtract and add corresponding values.
3. To remove bit at ith bit to i+1. we need to subtract i_bit<<i and add it at i+1 location for that we need to add i_bit<<(i+1).
4. Similarly do for (i+1)th bit. Remove it from i+1 to i.

## C++

 `// C++ program to swap even and``// odd bits of a given number``#include ``using` `namespace` `std;` `// Function to swap even``// and odd bits``unsigned ``int` `swapBits(unsigned ``int` `x)``{``    ``for``(``int` `i=0; i<32; i+=2){``        ``int` `i_bit = ( x >> i ) & 1; ``// find i th bit``        ``int` `i_1_bit = (x >> ( i+1 )) & 1;  ``// find i+1 th bit``        ` `        ``x = x - ( i_bit << i) ``// remove i_bit``              ``- ( i_1_bit << ( i+1 ) ) ``// remove i+1 th bit``              ``+ ( i_bit << ( i+1 ) ) ``// put i_bit at i+1 location``              ``+ ( i_1_bit << i );  ``// put i+1 bit at i location``    ``}``    ``return` `x;``}` `// Driver code``int` `main()``{``    ``unsigned ``int` `x =23; ``// 00010111` `    ``// Output is 43 (00101011)``    ``cout<

## Java

 `// Java program to swap even and``// odd bits of a given number``import` `java.io.*;` `class` `GFG {` `    ``// Function to swap even``    ``// and odd bits``    ``static` `int` `swapBits(``int` `x)``    ``{``        ``for` `(``int` `i = ``0``; i < ``32``; i += ``2``) {``            ``int` `i_bit = (x >> i) & ``1``; ``// find i th bit``            ``int` `i_1_bit``                ``= (x >> (i + ``1``)) & ``1``; ``// find i+1 th bit` `            ``x = x - (i_bit << i) ``// remove i_bit``                ``- (i_1_bit << (i + ``1``)) ``// remove i+1 th bit``                ``+ (i_bit``                   ``<< (i + ``1``)) ``// put i_bit at i+1 location``                ``+ (i_1_bit``                   ``<< i); ``// put i+1 bit at i location``        ``}``        ``return` `x;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `x = ``23``; ``// 00010111` `        ``// Output is 43 (00101011)``        ``System.out.print(swapBits(x));``    ``}``}` `// This code is contributed by subham348.`

## Python3

 `# Python program to swap even and``# odd bits of a given number` `# Function to swap even``# and odd bits``def` `swapBits(x):``  ` `    ``# Get all even bits of x``    ``even_bits ``=` `x & ``0xAAAAAAAA` `    ``# Get all odd bits of x``    ``odd_bits ``=` `x & ``0x55555555``    ` `    ``# Right shift even bits``    ``even_bits >>``=` `1``    ` `    ``# Left shift odd bits``    ``odd_bits <<``=` `1``    ``for` `i ``in` `range``(``0``,``32``,``2``):``        ``i_bit ``=` `(x >> ``1``) & ``1``; ``# find i th bit``        ``i_1_bit ``=` `(x >> (i ``+` `1``)) & ``1``; ``# find i+1 th bit``        ` `        ``x ``=` `x ``-` `(i_bit << i) ``# remove i_bit``        ``-` `(i_1_bit << (i ``+` `2``)) ``# remove i+1 th bit``        ``+` `(i_bit << (i ``+` `1``)) ``# put i_bit at i+1 location``        ``+` `(i_1_bit << i); ``# put i+1 bit at i location``    ` `    ``# Combine even and odd bits``    ``return` `(even_bits | odd_bits)` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``x ``=` `23``; ``# 00010111` `    ``# Output is 43 (00101011)``    ``print``(swapBits(x));`  `# This code is contributed by Rajput-Ji`

## C#

 `// C# program to swap even and``// odd bits of a given number``using` `System;` `class` `GFG {` `    ``// Function to swap even``    ``// and odd bits``    ``static` `int` `swapBits(``int` `x)``    ``{``        ``for` `(``int` `i = 0; i < 32; i += 2) {``            ``int` `i_bit = (x >> i) & 1; ``// find i th bit``            ``int` `i_1_bit``                ``= (x >> (i + 1)) & 1; ``// find i+1 th bit` `            ``x = x - (i_bit << i) ``// remove i_bit``                ``- (i_1_bit << (i + 1)) ``// remove i+1 th bit``                ``+ (i_bit``                   ``<< (i + 1)) ``// put i_bit at i+1 location``                ``+ (i_1_bit``                   ``<< i); ``// put i+1 bit at i location``        ``}``        ``return` `x;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int` `x = 23; ``// 00010111` `        ``// Output is 43 (00101011)``        ``Console.Write(swapBits(x));``    ``}``}` `// This code is contributed by subham348.`

## Javascript

 ``

Output:

` 43 `

Time Complexity: O(constant)

Auxiliary Space: O(1)

If we take a closer look at the example, we can observe that we basically need to right shift (>>) all even bits (In the above example, even bits of 23 are highlighted) by 1 so that they become odd bits (highlighted in 43), and left shift (<<) all odd bits by 1 so that they become even bits. The following solution is based on this observation. The solution assumes that input number is stored using 32 bits.
Let the input number be x
1) Get all even bits of x by doing bitwise and of x with 0xAAAAAAAA. The number 0xAAAAAAAA is a 32 bit number with all even bits set as 1 and all odd bits as 0.
2) Get all odd bits of x by doing bitwise and of x with 0x55555555. The number 0x55555555 is a 32 bit number with all odd bits set as 1 and all even bits as 0.
3) Right shift all even bits.
4) Left shift all odd bits.
5) Combine new even and odd bits and return.

## C++

 `// C++ program to swap even and``// odd bits of a given number``#include ``using` `namespace` `std;` `// Function to swap even``// and odd bits``unsigned ``int` `swapBits(unsigned ``int` `x)``{``    ``// Get all even bits of x``    ``unsigned ``int` `even_bits = x & 0xAAAAAAAA;` `    ``// Get all odd bits of x``    ``unsigned ``int` `odd_bits = x & 0x55555555;` `    ``even_bits >>= 1; ``// Right shift even bits``    ``odd_bits <<= 1; ``// Left shift odd bits` `    ``return` `(even_bits | odd_bits); ``// Combine even and odd bits``}` `// Driver code``int` `main()``{``    ``unsigned ``int` `x = 23; ``// 00010111` `    ``// Output is 43 (00101011)``    ``cout<

## C

 `// C program to swap even and``// odd bits of a given number``#include ` `// Function to swap even``// and odd bits``unsigned ``int` `swapBits(unsigned ``int` `x)``{``    ``// Get all even bits of x``    ``unsigned ``int` `even_bits = x & 0xAAAAAAAA;` `    ``// Get all odd bits of x``    ``unsigned ``int` `odd_bits  = x & 0x55555555;` `    ``even_bits >>= 1;  ``// Right shift even bits``    ``odd_bits <<= 1;   ``// Left shift odd bits` `    ``return` `(even_bits | odd_bits); ``// Combine even and odd bits``}` `// Driver program to test above function``int` `main()``{``    ``unsigned ``int` `x = 23; ``// 00010111` `    ``// Output is 43 (00101011)``    ``printf``(``"%u "``, swapBits(x));` `    ``return` `0;``}`

## Java

 `// Java program to swap even``// and odd bits of a given number` `class` `GFG{``    ` `    ``// Function to swap even``    ``// and odd bits``    ``static` `int` `swapBits(``int` `x)``    ``{``        ``// Get all even bits of x``        ``int` `even_bits = x & ``0xAAAAAAAA``;``    ` `        ``// Get all odd bits of x``        ``int` `odd_bits = x & ``0x55555555``;``    ` `        ``// Right shift even bits``        ``even_bits >>= ``1``;``        ` `        ``// Left shift even bits``        ``odd_bits <<= ``1``;``        ` `        ``// Combine even and odd bits``        ``return` `(even_bits | odd_bits);``    ``}``    ` `    ``// Driver program to test above function``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `x = ``23``; ``// 00010111``    ` `        ``// Output is 43 (00101011)``        ``System.out.println(swapBits(x));``    ``}``}` `// This code is contributed by Smitha Dinesh Semwal`

## Python 3

 `# Python 3 program to swap even``# and odd bits of a given number` `# Function for swapping even``# and odd bits``def` `swapBits(x) :``    ` `    ``# Get all even bits of x``    ``even_bits ``=` `x & ``0xAAAAAAAA` `    ``# Get all odd bits of x``    ``odd_bits ``=` `x & ``0x55555555``    ` `    ``# Right shift even bits``    ``even_bits >>``=` `1``    ` `    ``# Left shift odd bits``    ``odd_bits <<``=` `1` `    ``# Combine even and odd bits``    ``return` `(even_bits | odd_bits)`  `# Driver program``# 00010111``x ``=` `23` `# Output is 43 (00101011)``print``(swapBits(x))`  `# This code is contributed``# by Nikita Tiwari.`

## C#

 `// C# program to swap even and odd bits``// of a given number``using` `System;` `class` `GFG {``    ` `    ``// Function to swap even``    ``// and odd bits``    ``static` `long` `swapBits(``int` `x)``    ``{``        ``// Get all even bits of x``        ``long` `even_bits = x & 0xAAAAAAAA;``    ` `        ``// Get all odd bits of x``        ``long` `odd_bits = x & 0x55555555;``    ` `        ``// Right shift even bits``        ``even_bits >>= 1;``        ` `        ``// Left shift even bits``        ``odd_bits <<= 1;``        ` `        ``// Combine even and odd bits``        ``return` `(even_bits | odd_bits);``    ``}``    ` `    ``// Driver program to test above function``    ``public` `static` `void` `Main()``    ``{``        ` `        ``int` `x = 23; ``// 00010111``    ` `        ``// Output is 43 (00101011)``        ``Console.Write(swapBits(x));``    ``}``}` `// This code is contributed by Sam007.`

## PHP

 `>= 1;``    ` `    ``// Left shift odd bits``    ``\$odd_bits` `<<= 1;` `    ``// Combine even and odd bits``    ``return` `(``\$even_bits` `| ``\$odd_bits``);``}` `// Driver Code` `// 00010111``\$x` `= 23;` `// Output is 43 (00101011)``echo` `swapBits(``\$x``);` `// This code is contributed by Ajit``?>`

## Javascript

 ``

Output:

` 43 `

Time Complexity: O(1)

Auxiliary Space: O(1)