leetcode-476. Number Complement

476. Number Complement

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.

求一个数的补码。

 

public class Solution {
    private int getPow(int x,int y){
        int a=1;
        for(int i=0;i<y;i++){
            a*=x;
        }
        return a;
    }
    public int findComplement(int num) {
        int sum=0;
        if(num==0){
            return 1;
        }
        if(num>0){
            int i=0;
            while(num!=0){
                if(num%2==1){
                    i++;
                }else{
                    sum=sum+getPow(2,i);
                    i++;
                }
                num/=2;
            }
        }
        
        return sum;
    }
}

　　另一种解法:

举个例子:
100110, 它的补码是 011001, 和是 111111. 所以我们先求和num的二进制长度相同全为一的数，然后做减法

public int findComplement(int num) 
    {
        int i = 0;
        int j = 0;
        
        while (i < num)
        {
            i += Math.pow(2, j);
            j++;
        }
        
        return i - num;
    }