LeetCode 476. Number Complement(Java)

原题：
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.

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.

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题意：
给定一个正整数，输出它的补数。补数的策略是通过翻转二进位表示。

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思路：
1.求出该数的二进制位数；
2.通过给定数num和相同位数的二进制数（全为1）进行异或，即可求出补数。

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代码：

public class Solution {
    public int findComplement(int num) {
        int ans = 0;//the count of the num's bits
        int temp = num;//copy of the num
        while(temp != 0){
            ans++;
            temp /= 2;
        }
        return num ^ (int)(Math.pow(2,ans)-1);
    }
}