476. Number Complement

476. Number Complement

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: 5Output: 2Explanation: 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: 1Output: 0Explanation: 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); }}

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