[leetcode] problem 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.

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.

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.

public int (int num) {
    int mask = ~0;

    while ((num & mask) != 0)
        mask <<= 1;

    return ~num ^ mask;
}