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67 lines
1.7 KiB
Markdown
67 lines
1.7 KiB
Markdown
# [1009. Complement of Base 10 Integer](https://leetcode.com/problems/complement-of-base-10-integer/)
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## 题目
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The **complement** of an integer is the integer you get when you flip all the `0`'s to `1`'s and all the `1`'s to `0`'s in its binary representation.
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- For example, The integer `5` is `"101"` in binary and its **complement** is `"010"` which is the integer `2`.
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Given an integer `n`, return *its complement*.
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**Example 1:**
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```
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Input: n = 5
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Output: 2
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Explanation: 5 is "101" in binary, with complement "010" in binary, which is 2 in base-10.
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```
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**Example 2:**
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```
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Input: n = 7
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Output: 0
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Explanation: 7 is "111" in binary, with complement "000" in binary, which is 0 in base-10.
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```
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**Example 3:**
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```
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Input: n = 10
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Output: 5
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Explanation: 10 is "1010" in binary, with complement "0101" in binary, which is 5 in base-10.
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```
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**Constraints:**
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- `0 <= n < 109`
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## 题目大意
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每个非负整数 N 都有其二进制表示。例如， 5 可以被表示为二进制 "101"，11 可以用二进制 "1011" 表示，依此类推。注意，除 N = 0 外，任何二进制表示中都不含前导零。
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二进制的反码表示是将每个 1 改为 0 且每个 0 变为 1。例如，二进制数 "101" 的二进制反码为 "010"。
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给你一个十进制数 N，请你返回其二进制表示的反码所对应的十进制整数。
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## 解题思路
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- 简单题。求一个十进制数的反码，只需要让该数和全 1 的数进行异或计算即可。所以本题重点在如何构造 mask 上。
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## 代码
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```go
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package leetcode
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func bitwiseComplement(n int) int {
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mask := 1
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for mask < n {
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mask = (mask << 1) + 1
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}
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return mask ^ n
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}
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``` |