Related Articles

# Set all odd bits of a number

• Difficulty Level : Hard
• Last Updated : 03 May, 2021

Given a number, the task is to set all odd bits of a number. Positions of bits are counted from LSB (least significant bit) to MSB (Most significant bit). Position of LSB is considered as 1.

Examples :

```Input : 20
Output : 21
Explanation : Binary representation of 20
is 10100. Setting all odd
bits make the number 10101 which is binary
representation of 21.

Input : 10
Output : 15```

Method 1 (Using OR)
1. First generate a number that contains odd position bits.
2. Take OR with the original number. Note that 1 | 1 = 1 and 1 | 0 = 1.

Let’s understand this approach with below code.

## C++

 `// CPP code Set all odd bits``// of a number``#include ``using` `namespace` `std;` `// set all odd bit``int` `oddbitsetnumber(``int` `n)``{``    ``int` `count = 0;` `    ``// res for store 010101.. number``    ``int` `res = 0;` `    ``// generate number form of 010101.....till``    ``// temp size``    ``for` `(``int` `temp = n; temp > 0; temp >>= 1) {` `        ``// if bit is odd, then generate``        ``// number and or with res``        ``if` `(count % 2 == 0)``            ``res |= (1 << count);` `        ``count++;``    ``}` `    ``return` `(n | res);``}` `// Driver code``int` `main()``{``    ``int` `n = 10;``    ``cout << oddbitsetnumber(n);``    ``return` `0;``}`

## Java

 `// Java code to Set all odd``// bits of a number` `class` `GFG``{` `    ``// set all odd bit``    ``static` `int` `oddbitsetnumber(``int` `n)``    ``{``        ``int` `count = ``0``;` `        ``// res for store 010101.. number``        ``int` `res = ``0``;` `        ``// generate number form of``        ``// 010101.....till temp size``        ``for` `(``int` `temp = n; temp > ``0``; temp >>= ``1``)``        ``{` `            ``// if bit is odd, then generate``            ``// number and or with res``            ``if` `(count % ``2` `== ``0``)``                ``res |= (``1` `<< count);` `            ``count++;``        ``}` `        ``return` `(n | res);``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `n = ``10``;``        ``System.out.println(oddbitsetnumber(n));``    ``}``}` `// This code is contributed``// by prerna saini`

## Python3

 `''' Python3 code Set all odd bits``   ``of a number'''``   ` `# set all odd bit``def` `oddbitsetnumber(n):``    ``count ``=` `0``    ``# res for store 010101.. number``    ``res ``=` `0` `    ``# generate number form of 010101.....till``    ``# temp size``    ``temp ``=` `n``    ``while` `temp > ``0``:` `        ``# if bit is odd, then generate``        ``# number and or with res``        ``if` `count ``%` `2` `=``=` `0``:``            ``res |``=` `(``1` `<< count)` `        ``count ``+``=` `1``        ``temp >>``=` `1` `    ``return` `(n | res)` `n ``=` `10``print` `(oddbitsetnumber(n))` `#This code is contributed by Shreyanshi Arun.`

## C#

 `// C# code to Set all odd``// bits of a number``using` `System;` `class` `GFG``{``    ``static` `int` `oddbitsetnumber(``int` `n)``    ``{``        ``int` `count = 0;` `        ``// res for store 010101.. number``        ``int` `res = 0;` `        ``// generate number form of``        ``// 010101.....till temp size``        ``for` `(``int` `temp = n; temp > 0;``                           ``temp >>= 1)``        ``{` `            ``// if bit is odd, then``            ``// generate number and``            ``// or with res``            ``if` `(count % 2 == 0)``                ``res |= (1 << count);` `            ``count++;``        ``}` `        ``return` `(n | res);``    ``}``    ` `    ``// Driver Code``    ``static` `public` `void` `Main ()``    ``{``        ``int` `n = 10;``        ``Console.WriteLine(oddbitsetnumber(n));``    ``}``}` `// This code is contributed``// by prerna ajit`

## PHP

 ` 0; ``\$temp` `>>= 1)``    ``{` `        ``// if bit is odd, then generate``        ``// number and or with res``        ``if` `(``\$count` `% 2 == 0)``            ``\$res` `|= (1 << ``\$count``);` `        ``\$count``++;``    ``}` `    ``return` `(``\$n` `| ``\$res``);``}` `    ``// Driver code``    ``\$n` `= 10;``    ``echo` `oddbitsetnumber(``\$n``);` `// This code is contributed by mits``?>`

## Javascript

 ``

Output:

`15`

Method 2 (A O(1) solution for 32 bit numbers)

## C++

 `// Efficient CPP program to set all``// odd bits number``#include ``using` `namespace` `std;` `// return MSB set number``int` `getmsb(``int` `n)``{``    ``// set all bits including MSB.``    ``n |= n >> 1;``    ``n |= n >> 2;``    ``n |= n >> 4;``    ``n |= n >> 8;``    ``n |= n >> 16;` `    ``// return MSB``    ``return` `(n + 1) >> 1;``}` `// Returns a number of same size (MSB at``// same position) as n and all odd bits``// set.``int` `getevenbits(``int` `n)``{``    ``n = getmsb(n);` `    ``// generate odd bits like 010101..``    ``n |= n >> 2;``    ``n |= n >> 4;``    ``n |= n >> 8;``    ``n |= n >> 16;` `    ``// if bits is even then shift by 1``    ``if` `((n&1) == 0)``        ``n = n >> 1;``    ` `    ``// return odd set bits number``    ``return` `n; ``}` `// set all odd bits here``int` `setalloddbits(``int` `n)``{   ``    ``// take OR with odd set bits number``    ``return` `n | getevenbits(n);   ``}` `// Driver code``int` `main()``{``    ``int` `n = 10;``    ``cout << setalloddbits(n);``    ``return` `0;``}`

## Java

 `// Efficient Java program to set``// all odd bits number``class` `GFG {` `    ``// return MSB set number``    ``static` `int` `getmsb(``int` `n)``    ``{``        ``// set all bits including MSB.``        ``n |= n >> ``1``;``        ``n |= n >> ``2``;``        ``n |= n >> ``4``;``        ``n |= n >> ``8``;``        ``n |= n >> ``16``;` `        ``// return MSB``        ``return` `(n + ``1``) >> ``1``;``    ``}` `    ``// Returns a number of same``    ``// size (MSB at same position)``    ``// as n and all odd bits set.``    ``static` `int` `getevenbits(``int` `n)``    ``{``        ``n = getmsb(n);` `        ``// generate odd bits``        ``// like 010101..``        ``n |= n >> ``2``;``        ``n |= n >> ``4``;``        ``n |= n >> ``8``;``        ``n |= n >> ``16``;` `        ``// if bits is even``        ``// then shift by 1``        ``if` `((n & ``1``) == ``0``)``            ``n = n >> ``1``;` `        ``// return odd set bits number``        ``return` `n;``    ``}` `    ``// set all odd bits here``    ``static` `int` `setalloddbits(``int` `n)``    ``{``        ``// take OR with odd``        ``// set bits number``        ``return` `n | getevenbits(n);``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `n = ``10``;``        ``System.out.println(setalloddbits(n));``    ``}``}` `// This code is contributed``// by prerna saini`

## Python3

 `# Efficient python3 program to ``# set all odd bits number``import` `math` `# return MSB set number``def` `getmsb( n):` `    ``# set all bits including MSB.``    ``n |``=` `n >> ``1``    ``n |``=` `n >> ``2``    ``n |``=` `n >> ``4``    ``n |``=` `n >> ``8``    ``n |``=` `n >> ``16` `    ``# return MSB``    ``return` `(n ``+` `1``) >> ``1`  `# Returns a number of same``# size (MSB at same position)``# as n and all odd bits set.``def` `getevenbits(n):` `    ``n ``=` `getmsb(n)` `    ``# generate odd bits``    ``# like 010101..``    ``n |``=` `n >> ``2``    ``n |``=` `n >> ``4``    ``n |``=` `n >> ``8``    ``n |``=` `n >> ``16` `    ``# if bits is even``    ``# then shift by 1``    ``if` `((n & ``1``) ``=``=` `0``):``        ``n ``=` `n >> ``1``    ` `    ``# return odd set bits number``    ``return` `n`  `# set all odd bits here``def` `setalloddbits( n):` `    ``# take OR with odd``    ``# set bits number``    ``return` `n | getevenbits(n)`  `# Driver Program``n ``=` `10``print``(setalloddbits(n))``    `  `# This code is contributed``# by Gitanjali.`

## C#

 `// Efficient C# program to``// set all odd bits number``using` `System;` `class` `GFG``{``    ` `    ``// return MSB set number``    ``static` `int` `getmsb(``int` `n)``    ``{``        ``// set all bits``        ``// including MSB.``        ``n |= n >> 1;``        ``n |= n >> 2;``        ``n |= n >> 4;``        ``n |= n >> 8;``        ``n |= n >> 16;` `        ``// return MSB``        ``return` `(n + 1) >> 1;``    ``}``    ` `    ``// Returns a number of same``    ``// size (MSB at same position)``    ``// as n and all odd bits set.``    ``static` `int` `getevenbits(``int` `n)``    ``{``        ``n = getmsb(n);` `        ``// generate odd bits``        ``// like 010101..``        ``n |= n >> 2;``        ``n |= n >> 4;``        ``n |= n >> 8;``        ``n |= n >> 16;` `        ``// if bits is even``        ``// then shift by 1``        ``if` `((n & 1) == 0)``            ``n = n >> 1;` `        ``// return odd``        ``// set bits number``        ``return` `n;``    ``}` `    ``// set all odd bits here``    ``static` `int` `setalloddbits(``int` `n)``    ``{``        ``// take OR with odd``        ``// set bits number``        ``return` `n | getevenbits(n);``    ``}` `    ``// Driver Code``    ``static` `public` `void` `Main ()``    ``{``        ``int` `n = 10;``        ``Console.WriteLine(setalloddbits(n));``    ``}``}` `// This code is contributed ajit`

## PHP

 `> 1;``    ``\$n` `|= ``\$n` `>> 2;``    ``\$n` `|= ``\$n` `>> 4;``    ``\$n` `|= ``\$n` `>> 8;``    ``\$n` `|= ``\$n` `>> 16;` `    ``// return MSB``    ``return` `(``\$n` `+ 1) >> 1;``}` `// Returns a number of``// same size (MSB at``// same position) as n``// and all odd bits set``function` `getevenbits(``\$n``)``{``    ``\$n` `= getmsb(``\$n``);` `    ``// generate odd bits``    ``// like 010101..``    ``\$n` `|= ``\$n` `>> 2;``    ``\$n` `|= ``\$n` `>> 4;``    ``\$n` `|= ``\$n` `>> 8;``    ``\$n` `|= ``\$n` `>> 16;` `    ``// if bits is even``    ``// then shift by 1``    ``if` `((``\$n``&1) == 0)``        ``\$n` `= ``\$n` `>> 1;``    ` `    ``// return odd set``    ``// bits number``    ``return` `\$n``;``}` `// set all odd bits here``function` `setalloddbits(``\$n``)``{``    ` `    ``// take OR with odd``    ``// set bits number``    ``return` `\$n` `| getevenbits(``\$n``);``}` `    ``// Driver code``    ``\$n` `= 10;``    ``echo` `setalloddbits(``\$n``);` `// This code is contributed by mits``?>`

## Javascript

 ``

Output:

`15`

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

My Personal Notes arrow_drop_up