Php interview questions (calculate the number of '1' after a decimal number is converted to binary)

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This is an interview question I encountered yesterday.

At first glance, it is quite simple, but it cannot be implemented in detail.

After returning home, Baidu found an answer.

As follows:

// Calculate the number of '1' in a decimal number and convert it to binary number. // for example, if decimal 11 = binary 1011, the result is 3 1. // solution: use n & (n-1) to change the last 1 to 0 // xxxx1000 & (xxxx1000-1) = xxxx1000 & xxxx0111 = xxxx0000 // 1011 & (1011-1) = 1011 & 1010 = 1010 // until the last 1 is 0, the result is: 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 easy to understand (my bit operations are not good at learning ...)

I thought about the solution below:

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

This should be easier to understand.

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