LeetCode. 476. Number Complement

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.

分析：

给定一个正整数，按位取反， 比如题目中给出的5，二进制为101，那么取反就是010, 010对应的十进制数是2.

实现这个功能的话，按位取反，很容易想到异或操作符^, 将原数比如101与111进行抑或操作，那么所得结果就是010.也就是我们需要的。

代码实现：

function complement(number) {
    var mask = 1;
    var temp = number;
    while( temp > 0) {
        temp = temp >> 1;
        mask = mask << 1;
    }
    return number ^ (mask-1);
}
complement(1);

这里 mask-1是为了取111...值。