Single Number II

Given an array of integers, every element appears three times except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

public class Solution {
    public int singleNumber(int[] A) {
        int ones = 0;
        int twos = 0;
        int not_threes=0, x=0;

        for (int i=0; i<A.length; ++i) {
            x =  A[i];
            twos |= ones & x;
            ones ^= x;
            not_threes = ~(ones & twos);
            ones &= not_threes;
            twos &= not_threes;
        }
        return twos!=0?twos:ones;
        
    }
}