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?

Solution:

public class Solution {
  public int singleNumber(int[] nums) {
    int ones = 0, twos = 0, threes = 0;
    for (int i = 0; i < nums.length; i++) {
      // twos holds the num that appears twice
      twos |= ones & nums[i];
      // ones holds the num that appears once
      ones ^= nums[i];
      // threes holds the num that appears three times
      threes = ones & twos;
      // if num[i] appears three times
      // doing this will clear ones and twos
      ones &= ~threes;
      twos &= ~threes;
    }
    return ones;
  }
}