# Toggle first and last bits of a number

Given a number n, the task is to toggle only first and last bits of a number

Examples :

```Input : 10
Output : 3
Binary representation of 10 is
1010. After toggling first and
last bits, we get 0011.

Input : 15
Output : 6
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Prerequisite : Find MSB of given number.

1) Generate a number which contains first and last bit as set. We need to change all middle bits to 0 and keep corner bits as 1.

2) Answer is XOR of generated number and original number.

## C++

 `// CPP program to toggle first and last  ` `// bits of a number ` `#include ` `using` `namespace` `std; ` ` `  `// Returns a number which has same bit ` `// count as n and has only first and last  ` `// bits as set. ` `int` `takeLandFsetbits(``int` `n) ` `{ ` `    ``// set all the bit of the number ` `    ``n |= n >> 1; ` `    ``n |= n >> 2; ` `    ``n |= n >> 4; ` `    ``n |= n >> 8; ` `    ``n |= n >> 16; ` ` `  `    ``// Adding one to n now unsets ` `    ``// all bits and moves MSB to  ` `    ``// one place. Now we shift  ` `    ``// the number by 1 and add 1. ` `    ``return` `((n + 1) >> 1) + 1; ` `} ` ` `  `int` `toggleFandLbits(``int` `n) ` `{ ` `    ``// if number is 1 ` `    ``if` `(n == 1) ` `        ``return` `0; ` ` `  `    ``// take XOR with first and ` `    ``// last set bit number ` `    ``return` `n ^ takeLandFsetbits(n); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 10; ` `    ``cout << toggleFandLbits(n); ` `    ``return` `0; ` `} `

## Java

 `// Java program to toggle first and last  ` `// bits of a number ` `import` `java.io.*; ` ` `  `class` `GFG { ` `     `  `    ``// Returns a number which has same bit ` `    ``// count as n and has only first and last  ` `    ``// bits as set. ` `    ``static` `int` `takeLandFsetbits(``int` `n) ` `    ``{ ` `        ``// set all the bit of the number ` `        ``n |= n >> ``1``; ` `        ``n |= n >> ``2``; ` `        ``n |= n >> ``4``; ` `        ``n |= n >> ``8``; ` `        ``n |= n >> ``16``; ` `      `  `        ``// Adding one to n now unsets ` `        ``// all bits and moves MSB to  ` `        ``// one place. Now we shift  ` `        ``// the number by 1 and add 1. ` `        ``return` `((n + ``1``) >> ``1``) + ``1``; ` `    ``} ` `      `  `    ``static` `int` `toggleFandLbits(``int` `n) ` `    ``{ ` `        ``// if number is 1 ` `        ``if` `(n == ``1``) ` `            ``return` `0``; ` `      `  `        ``// take XOR with first and ` `        ``// last set bit number ` `        ``return` `n ^ takeLandFsetbits(n); ` `    ``} ` `      `  `    ``// Driver code ` `    ``public` `static` `void` `main(String args[]) ` `    ``{ ` `        ``int` `n = ``10``; ` `        ``System.out.println(toggleFandLbits(n)); ` `    ``} ` `} ` ` `  `/*This code is contributed by Nikita Tiwari.*/`

## Python3

 `# Python 3 program to toggle first ` `#  and last bits of a number. ` ` `  ` `  `# Returns a number which has same bit ` `# count as n and has only first and last  ` `# bits as set. ` `def` `takeLandFsetbits(n) : ` `     `  `# set all the bit of the number ` `    ``n ``=` `n | n >> ``1` `    ``n ``=` `n | n >> ``2` `    ``n ``=` `n | n >> ``4` `    ``n ``=` `n | n >> ``8` `    ``n ``=` `n | n >> ``16` ` `  `    ``# Adding one to n now unsets ` `    ``# all bits and moves MSB to  ` `    ``# one place. Now we shift  ` `    ``# the number by 1 and add 1. ` `    ``return` `((n ``+` `1``) >> ``1``) ``+` `1` `     `  `def` `toggleFandLbits(n) : ` `    ``# if number is 1 ` `    ``if` `(n ``=``=` `1``) : ` `        ``return` `0` ` `  `    ``# take XOR with first and ` `    ``# last set bit number ` `    ``return` `n ^ takeLandFsetbits(n) ` ` `  `# Driver code ` `n ``=` `10` `print``(toggleFandLbits(n)) ` ` `  `# This code is contributed by Nikita Tiwari. `

## C#

 `// C# program to toggle first and last  ` `// bits of a number ` `using` `System; ` ` `  `class` `GFG { ` `      `  `    ``// Returns a number which has same bit ` `    ``// count as n and has only first and last  ` `    ``// bits as set. ` `    ``static` `int` `takeLandFsetbits(``int` `n) ` `    ``{ ` `        ``// set all the bit of the number ` `        ``n |= n >> 1; ` `        ``n |= n >> 2; ` `        ``n |= n >> 4; ` `        ``n |= n >> 8; ` `        ``n |= n >> 16; ` `       `  `        ``// Adding one to n now unsets ` `        ``// all bits and moves MSB to  ` `        ``// one place. Now we shift  ` `        ``// the number by 1 and add 1. ` `        ``return` `((n + 1) >> 1) + 1; ` `    ``} ` `       `  `    ``static` `int` `toggleFandLbits(``int` `n) ` `    ``{ ` `         `  `        ``// if number is 1 ` `        ``if` `(n == 1) ` `            ``return` `0; ` `       `  `        ``// take XOR with first and ` `        ``// last set bit number ` `        ``return` `n ^ takeLandFsetbits(n); ` `    ``} ` `       `  `    ``// Driver code ` `    ``public` `static` `void` `Main() ` `    ``{ ` `         `  `        ``int` `n = 10; ` `         `  `        ``Console.WriteLine(toggleFandLbits(n)); ` `    ``} ` `} ` `  `  `// This code is contributed by Anant Agarwal. `

## PHP

 `> 1; ` `    ``\$n` `|= ``\$n` `>> 2; ` `    ``\$n` `|= ``\$n` `>> 4; ` `    ``\$n` `|= ``\$n` `>> 8; ` `    ``\$n` `|= ``\$n` `>> 16; ` ` `  `    ``// Adding one to n now unsets ` `    ``// all bits and moves MSB to  ` `    ``// one place. Now we shift  ` `    ``// the number by 1 and add 1. ` `    ``return` `((``\$n` `+ 1) >> 1) + 1; ` `} ` ` `  `function` `toggleFandLbits(int ``\$n``) ` `{ ` `    ``// if number is 1 ` `    ``if` `(``\$n` `== 1) ` `        ``return` `0; ` ` `  `    ``// take XOR with first and ` `    ``// last set bit number ` `    ``return` `\$n` `^ takeLandFsetbits(``\$n``); ` `} ` ` `  `// Driver code ` `\$n` `= 10; ` `echo` `toggleFandLbits(``\$n``); ` ` `  `// This code is contributed by mits  ` `?> `

Output :

```3
```

Time Complexity is O(1).

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