1009. Complement of Base 10 Integer #

题目 #

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.

• For example, The integer 5 is "101" in binary and its complement is "010" which is the integer 2.

Given an integer n, return its complement.

Example 1:

Input: n = 5
Output: 2
Explanation: 5 is "101" in binary, with complement "010" in binary, which is 2 in base-10.

Example 2:

Input: n = 7
Output: 0
Explanation: 7 is "111" in binary, with complement "000" in binary, which is 0 in base-10.

Example 3:

Input: n = 10
Output: 5
Explanation: 10 is "1010" in binary, with complement "0101" in binary, which is 5 in base-10.

Constraints:

• 0 <= n < 109

题目大意 #

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。

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”。

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。

解题思路 #

• 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。

代码 #

package leetcode

func bitwiseComplement(n int) int {
    mask := 1 
    for mask < n {
        mask = (mask << 1) + 1
    }
    return mask ^ n
}