LeetCode Number Complement

原题链接在这里：https://leetcode.com/problems/number-complement/

题目：

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.

题解：

找到num最左面的1 bit, 从这个位置到最后是要flip的部分. template是从最左位置到最后到时1 bit. 

flip原来整体的num, 然后位运算 & template.

Time Complexity: O(1). Space: O(1).

AC Java:

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