leetcode 476: Number Complement

原题：

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.

大意就是，找出这个数取反之后的数，是一个前置位不存在的取反。

代码如下：

int findComplement(int num) {    int t=1;    while(1)    {        if(num>t)            t=1+t*2;        else            break;    }    return (num^INT_MAX)-(INT_MAX-t);}

异或取反以后，把前置位减去就好了。