476.md

Question:

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.

Analysis

这道题是求一个数截去前面的0之后，取反后的大小。换个思路，假设本来是三位的，用2^3减去它就可以了，还是比较容易的。这里取了一个巧，就是记录出只有一个1的情况，比如101，搞成100后，记录下来，那高一位的就是1000了。

Tips

temp &= temp - 1 去除最后的一个1

Code

func findComplement(num int) int {
        temp := num
        var last int
        for temp != 0 {
                last = temp
                temp &= temp - 1
        }
        return last<<1 - 1 - num
}