leetcode_476

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

Example 1:

Input: num = 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: num = 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.

Constraints:

The given integer num is guaranteed to fit within the range of a 32-bit signed integer. num >= 1 You could assume no leading zero bit in the integer’s binary representation. This question is the same as 1009: https://leetcode.com/problems/complement-of-base-10-integer/

Solutions

1. straight forward

2. 0101 ^ 0111

class Solution {
public:
    int findComplement(int num) {
        if (num == 0) return 1;
        int n = num, c = 0;
        while (n) {
            n >>= 1;
            c = (c << 1) | 1;
        }
        return c ^ num;
    }
};