476. Number Complement

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.

首先得到输入的整数的二进制有x位，再将输入的输与x位的1按位异或

C++（6ms）：

 1 class Solution {
 2 public:
 3     int findComplement(int num) {
 4        int a = ~0 ;
 5        while(num&a){
 6           a<<=1;
 7        }
 8        a=~a;
 9        return num^a;
10     }
11 };

Integer.highestOneBit(int i)的作用

返回的则是跟它最靠近的比它小的2的N次方

也就是去掉低位的1，只保留最高位的1

java(11ms):

1 class Solution {
2     public int findComplement(int num) {
3         return ~num + (Integer.highestOneBit(num)<<1) ;
4     }
5 }