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.

这两个数相加是 2^n - 1 这种形式的所以可以这个么做

class Solution {
public:
    int findComplement(int num) {
        int n = 0;
        while (n < num) {
            n = (n<<1)|1;
        }
        return n - num;
    }
};

476. Number Complement

原文：http://www.cnblogs.com/pk28/p/7246898.html