[LeetCode] 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, twos = 0, threes = 0;          for(int i = 0; i < A.length; i++)          {              threes = twos & A[i];               twos = twos | ones & A[i];              ones = ones | A[i];                            twos = twos & ~threes;              ones = ones & ~threes;         }          return ones;      }}