476. Number Complement

Posted 2022-08-03 wx62ea2466cca9a

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:
The given integer is guaranteed to fit within the range of a 32-bit signed integer.
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.

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。

例如：5的二进制是101，我们的构造的掩码为mask=111，两者异或则为010，即是所要的结果。

public class Solution 
    public int findComplement(int num) 
        int mask = 1, temp = num;
        while(temp > 0) 
            mask = mask << 1;
            temp = temp >> 1;
        
        return num^(mask-1);