LeetCode 476. Number Complement

题目描述：

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.

就是简单的按位取反，不过不能把前导零给取反了，所以要先确定最高位所在的位置，取反后将更高位置零。

class Solution {
public:
    int findComplement(int num) {
        unsigned int unum = num;
        int sigbit = 0;
        while(unum){
            unum >>= 1;
            sigbit++;
        }
        unum = ~num;
        unum = unum << (32 - sigbit) >> (32 - sigbit);
        return (int)unum;
    }
};