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68 lines
1.8 KiB
Markdown
Executable File
68 lines
1.8 KiB
Markdown
Executable File
# [476. Number Complement](https://leetcode.com/problems/number-complement/)
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## 题目
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Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.
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**Note**:
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1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
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2. You could assume no leading zero bit in the integer’s binary representation.
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**Example 1**:
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Input: 5
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Output: 2
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Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.
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**Example 2**:
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Input: 1
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Output: 0
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Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.
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## 题目大意
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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。
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注意:
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给定的整数保证在32位带符号整数的范围内。
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你可以假定二进制数不包含前导零位。
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## 解题思路
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- 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。
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## 代码
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```go
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package leetcode
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// 解法一
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func findComplement(num int) int {
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xx := ^0 // ^0 = 1111111111111111111111
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for xx&num > 0 {
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xx <<= 1 // 构造出来的 xx = 1111111…000000，0 的个数就是 num 的长度
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}
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return ^xx ^ num // xx ^ num，结果是前面的 0 全是 1 的num，再取反即是答案
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}
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// 解法二
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func findComplement1(num int) int {
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temp := 1
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for temp <= num {
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temp <<= 1 // 构造出来的 temp = 00000……10000，末尾 0 的个数是 num 的长度
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}
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return (temp - 1) ^ num // temp - 1 即是前面都是 0，num 长度的末尾都是 1 的数，再异或 num 即是最终结果
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}
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``` |