一、題目描述

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.
 

思路：這種題沒什麼辦法，記住這個套路吧。舉個例子，num = 00000101時，另mask = ~0 = 11111111，讓mask變為 11111000，然後計算~mask & ~num即可得到結果

程式碼：

class Solution {
public:
    int findComplement(int num) {
        unsigned mask = ~0;
        while(mask & num){
            mask = mask << 1;
        }
        return ~mask & ~num;
        
    }
};