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: 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:

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.
分析：mask – 1为和num二进制位等长的所有位数为1的数，与num取^可以得到和num相反的数字。

 1 class Solution {
 2 public:
 3     int findComplement(int num) {
 4         int temp = num, mask = 1;
 5         while(temp){
 6             temp >>= 1;
 7             mask <<= 1;
 8         }
 9         return ((mask - 1) ^ num);
10     }
11 };

476. Number Complement

原文：http://www.cnblogs.com/qinduanyinghua/p/6341582.html