476. Number Complement

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.

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）：

class Solution {
public:
    int findComplement(int num) {
       int a = ~0 ;
       while(num&a){
          a<<=1;
       }
       a=~a;
       return num^a;
    }
};

 

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):

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