LeetCode 476 Number Complement（位运算）

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: 5Output: 2Explanation: 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: 1Output: 0Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

题目大意：求某个数的二进制反码。如5的二进制为101，它的反码就是010，也就是2。

解题思路：先利用(1 << (int)(log2(num) + 1)) - 1求出与num二进制位数相同且全为1的数，然后再用其与num进行异或运算即可。

代码如下：

int findComplement(int num) {    return ((1 << (int)(log2(num) + 1)) - 1) ^ num;}