leetcode 476. Number Complement题解

最新推荐文章于 2021-12-27 12:02:55 发布

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#二进制运算

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本文介绍了一种针对正整数求其补码的方法。通过翻转输入整数的二进制表示中的每一位来获得补码。文章给出了具体的C++实现代码，并提供了两个示例：输入5时输出2，输入1时输出0。

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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.

class Solution {
public:
    int findComplement(int num) {
        unsigned int mask = ~0;  // mask = 1111...
        while (num & mask) mask <<= 1; // 直到最高位
        // int直接求反会把最高位由0变为1成为负数
        // 题目要求no leading zero bit in the integer’s binary representation
        return ~num & ~mask; 
    }
};