LeetCode 476. Number Complement

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:

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

Example 2:

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

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【题目分析】

给定一个正整数，对该数的二进制表示形式，从最高位的1开始向后按位取反。

【思路】

如果我们能知道该数最高位的1所在的位置，就可以构造一个长度和该数据所占位置一样长的一个掩码mask，然后概述和mask进行异或即可。

class Solution {public: int findComplement(int num) { int ans = 1; int tmp = num; while(tmp != 0){ tmp = tmp >> 1; ans = ans << 1; } return (ans - 1) ^ num;            }};