476. Number Complement

主要内容：

• Leetcode题目，类型[Bit Manipulation]
• Java语言实现

题目

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.

实现

代码实现：git地址，可以关注我github地址，持续更新Leetcode代码实现。
题目的意思是，求一个数二进制表示的补数。不难看出，与输入值位数相同且bit值均为1的数与输入值进行异或后，会得到结果。例如example 1中101对应的比较数是111，111与101异或后得到010即结果。

第一种

    /**
      * 假设num二进制表示为n位，则循环结束后comp是10...0(n-1位0)，
      * 减1就得到和num位数相同且bit值都是1的数
    */
    public int findComplement(int num) {
        int temp = num,comp = 1;
        while(temp != 0){
            temp >>= 1;
            comp <<= 1;
        }
        return (comp - 1) ^ num;
    }