Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:

  1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
  2. You could assume no leading zero bit in the integer’s binary representation.

Example 1:

1
2
3
Input: 5
Output: 2
Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.

Example 2:

1
2
3
Input: 1
Output: 0
Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

思路

题目要求我们找到一个数的补码，我们首先要知道这个数是几位的二进制数；接下来要给这个二进制数加上一个掩码（Mask）以保证得到的二进制数在给定的位数范围内。一个数的补码就是这个数的取反+1，因此很容易得到结果。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
import math
class Solution(object):
    def findComplement(self, num):
        """
        :type num: int
        :rtype: int
        """
        if (num == 0):
            return 0
        else:
            digit = int(math.log(num,2)) + 1
            mask = 2 ** digit - 1
            comp = (-num-1) & mask
            return comp