# [476. Number Complement](https://leetcode.com/problems/number-complement/)


## 题目

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.


## 题目大意

给定一个正整数，输出它的补数。补数是对该数的二进制表示取反。

注意:

给定的整数保证在32位带符号整数的范围内。
你可以假定二进制数不包含前导零位。



## 解题思路


- 求一个正数的补数，补数的定义是对该数的二进制表示取反。当前不能改变符号位。按照题意构造相应的 mask 再取反即可。