# Previous smaller integer having one less number of set bits

Given a positive integer ‘n’ having ‘x’ number of set bits in its binary representation. The problem is to find the previous smaller integer(greatest integer smaller than n), having (x-1) number of set bits in its binary representation.

Note: 1 <= n

Examples :

```Input : 8
Output : 0
(8)10 = (1000)2
is having 1 set bit.

(0)10 = (0)2
is having 0 set bit and is the previous smaller.

Input : 25
Output : 24
```

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

Following are the steps:

1. Find the position of the rightmost set bit(considering last bit at position 1, second last bit at position 2 and so on) in the binary representation of n. Let the position be represented by pos. Refer this post.
2. Turn off or unset the bit at position pos. Refer this post.

## C++

 `// C++ implementation to find the previous  ` `// smaller integer with one less number of ` `// set bits ` `#include ` `using` `namespace` `std; ` ` `  `// function to find the position of  ` `// rightmost set bit. ` `int` `getFirstSetBitPos(``int` `n) ` `{ ` `    ``return` `log2(n & -n) + 1; ` `} ` ` `  `// function to find the previous smaller ` `// integer ` `int` `previousSmallerInteger(``int` `n) ` `{ ` `    ``// position of rightmost set bit of n ` `    ``int` `pos = getFirstSetBitPos(n); ` ` `  `    ``// turn off or unset the bit at  ` `    ``// position 'pos' ` `    ``return` `(n & ~(1 << (pos - 1))); ` `} ` ` `  `// Driver program ` `int` `main() ` `{ ` `    ``int` `n = 25; ` `    ``cout << previousSmallerInteger(n); ` `    ``return` `0; ` `} `

## Java

 `// Java implementation to find the previous ` `// smaller integer with one less number of ` `// set bits ` `class` `GFG { ` `     `  `    ``// function to find the position of ` `    ``// rightmost set bit. ` `    ``static` `int` `getFirstSetBitPos(``int` `n) ` `    ``{ ` `        ``return` `(``int``)(Math.log(n & -n) / Math.log(``2``)) + ``1``; ` `    ``} ` ` `  `    ``// function to find the previous smaller ` `    ``// integer ` `    ``static` `int` `previousSmallerInteger(``int` `n) ` `    ``{ ` `         `  `        ``// position of rightmost set bit of n ` `        ``int` `pos = getFirstSetBitPos(n); ` ` `  `        ``// turn off or unset the bit at ` `        ``// position 'pos' ` `        ``return` `(n & ~(``1` `<< (pos - ``1``))); ` `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``int` `n = ``25``; ` `        ``System.out.print(``"Previous smaller Integer ="`  `                     ``+ previousSmallerInteger(n)); ` `    ``} ` `} ` ` `  `// This code is contributed by Anant Agarwal. `

## Python3

 `# Python3 implementation to find  ` `# the previous smaller integer with ` `# one less number of set bits ` `import` `math ` ` `  `# Function to find the position   ` `# of rightmost set bit. ` `def` `getFirstSetBitPos(n): ` ` `  `    ``return` `(``int``)(math.log(n & ``-``n) ``/`  `                 ``math.log(``2``)) ``+` `1` ` `  `# Function to find the   ` `# previous smaller integer ` `def` `previousSmallerInteger(n): ` ` `  `    ``# position of rightmost set bit of n ` `    ``pos ``=` `getFirstSetBitPos(n) ` ` `  `    ``# turn off or unset the bit   ` `    ``# at position 'pos' ` `    ``return` `(n & ~(``1` `<< (pos ``-` `1``))) ` `     `  `# Driver code ` `n ``=` `25` `print``(``"Previous small Integer = "``, ` `       ``previousSmallerInteger(n)) ` `        `  `# This code is contributed by Anant Agarwal. `

## C#

 `// C# implementation to find the previous  ` `// smaller integer with one less number of ` `// set bits ` `using` `System; ` ` `  `    ``class` `GFG { ` `         `  `    ``// function to find the position of  ` `    ``// rightmost set bit. ` `    ``static` `int` `getFirstSetBitPos(``int` `n) ` `    ``{ ` `        ``return` `(``int``)(Math.Log(n & -n) /  ` `                           ``Math.Log(2)) + 1; ` `    ``} ` `      `  `    ``// function to find the previous smaller ` `    ``// integer ` `    ``static` `int` `previousSmallerInteger(``int` `n) ` `    ``{ ` `         `  `        ``// position of rightmost set bit of n ` `        ``int` `pos = getFirstSetBitPos(n); ` `      `  `        ``// turn off or unset the bit at  ` `        ``// position 'pos' ` `        ``return` `(n & ~(1 << (pos - 1))); ` `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `Main() ` `    ``{ ` `        ``int` `n = 25; ` `         `  `        ``Console.WriteLine(``"Previous small Integer ="` `                      ``+ previousSmallerInteger(n)); ` `    ``} ` `} ` ` `  `// This code is contributed by anant321. `

## PHP

 ` `

Output :

```Previous smaller integer = 24
```

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