lintcode-easy-Count 1 in Binary

Count how many

1

in binary representation of a 32-bit integer.

Example

Given

32

, return

1

Given

5

, return

2

Given

1023

, return

9

Challenge

If the integer is n bits with m 1 bits. Can you do it in O(m) time?

不知道怎么做challenge……

public class Solution {
/**
* @param num: an integer
* @return: an integer, the number of ones in num
*/
public int countOnes(int num) {
// write your code here
int count = 0;

for(int i = 0; i < 32; i++){
if(((num >> i) & 1) == 1)
count++;
}

return count;
}
};