PHP interview question (calculate the number of '1's in a decimal number after converting it to binary)



This is an interview question I encountered during an interview yesterday.

It seems simple at first glance, but it just can’t be realized in the details.

After returning home, I searched on Baidu and found an answer.

It is as follows:

//计算一个十进制数转换为二进制数中‘1’的个数
 //例如十进制11 = 二进制1011，则结果是3个1
 
    //解题思路：利用 n & (n - 1) 可以将最后一个1变0
   //xxxx1000 & (xxxx1000 - 1) = xxxx1000 & xxxx0111 = xxxx0000
   // 1011 & (1011 - 1) = 1011 & 1010 = 1010
   //直到最后一个1被与为0，得出结果
 function count1($n) {
        $r = 0;
        while ($n != 0) {
             $r++;
             $n &= ($n - 1);
         }
 
        return $r;
    }
 
     echo count1(11); 

After reading it, I think it is not very easy to understand (I am not good at bit operations...)

I thought about it for a while, and I have the following solution:

function count1($n) {
   $r = 0; 
	while($n !=0)
	{ 	
		
		if(($n%2) !=0 )
		{
			$r++;
		}
         $n=$n/2;
    }
	
	return $r;
}
    echo count1(8);

This should be much easier to understand.

The above introduces a PHP interview question (calculating the number of '1's in a decimal number after converting it to binary), including relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.