Count 1 in Binary – Python 3 (Week 13 -08)

class Solution:
    """
    @param: num: An integer
    @return: An integer
    """
    def countOnes(self, num):
        # write your code here
        if num < 0:
            num &= 1 << 32 - 1
        count = 0
        while num != 0:
            num &= num - 1
            count += 1
            
        return count

Python的整数是无限长的, -1在Java/C++的32位整数中为: 11...11111 (32个1)
但是在Python中为: ...1111111111111 (无限个1)
因此在遇到负数时要先截断为32位
num &= (1 << 32)-1