PHP Program to Count set bits in an integer

Write an efficient program to count number of 1s in binary representation of an integer.

Examples :

Input : n = 6
Output : 2
Binary representation of 6 is 110 and has 2 set bits

Input : n = 13
Output : 3
Binary representation of 11 is 1101 and has 3 set bits

setbit

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

1. Simple Method Loop through all bits in an integer, check if a bit is set and if it is then increment the set bit count. See below program.

PHP

<?php 
// Function to get no of set   
// bits in binary representation  
// of positive integer n  
function countSetBits($n) 
{ 
    $count = 0; 
    while ($n) 
    { 
        $count += $n & 1; 
        $n >>= 1; 
    } 
    return $count; 
} 
  
// Driver Code 
$i = 9; 
echo countSetBits($i); 
  
// This code is contributed by ajit 
?> 

Output:

Recursive Approach :

PHP

<?php 
// PHP implementation of recursive 
// approach to find the number of  
// set bits in binary representation 
// of positive integer n 
  
// recursive function  
// to count set bits 
function countSetBits($n) 
{ 
    // base case 
    if ($n == 0) 
        return 0; 
  
    else
  
        // if last bit set  
        // add 1 else add 0 
        return ($n & 1) +  
                countSetBits($n >> 1); 
} 
  
// Driver code 
  
// get value from user 
$n = 9; 
  
// function calling 
echo countSetBits($n); 
  
// This code is contributed by m_kit. 
?> 

Output:

Please refer complete article on Count set bits in an integer for more details!

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