leetcode476. Number Complement

476. Number Complement

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:
The given integer is guaranteed to fit within the range of a 32-bit signed integer.
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.

解法

取最高位为1时的数再减一，比如5（101），3位数，最高位为1时，即100，值为4（100），4－1＝3（011），7取反（010），再相与，即为010。

public class Solution {
    public int findComplement(int num) {
        return ~num & (Integer.highestOneBit(num) - 1);
    }
}