365. Count 1 in BinaryLintCode java

Posted 2020-12-04 phdeblog

Description

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?

解题：很简单，但是要考虑范围的问题。代码如下：

public class Solution {
    /*
     * @param num: An integer
     * @return: An integer
     */
    public int countOnes(int num) {
        // write your code here
        int count = 0;
        long temp = (long)num;
        if(temp < 0){
            temp = (long)Math.pow(2,32) + temp;
        }
        while(temp != 0){
            if(temp %2 == 1)
                count++;
            temp = temp / 2;
        }
        return count;
    }
};