Single Number II

Given an array of integers, every element appears thrice except for one which occurs once.

Find that element which does not appear thrice.

Could you implement it without using extra memory?

Input : [1, 2, 4, 3, 3, 2, 2, 3, 1, 1]
Output : 4

Method:

There are 32 bits in an integer, if a number appears thrice, then the bits for that number should appear as a multiple of 3 as well.

Solution:

Time: O(n)
Space: O(1)

public class Solution {
    // DO NOT MODIFY THE LIST. IT IS READ ONLY
    public int singleNumber(final List<Integer> A) {
        int totalBits = 32;
        int result = 0;
        int currentBit = 1;
        while (totalBits >= 0) {
            int count = 0;
            for (int n : A) {
                if ((currentBit & n) >= 1) {
                    count ++;
                }
            }
            if (count % 3 == 1) {
                result |= currentBit;
            }
            currentBit <<= 1;
            totalBits --;
        }
        return result;
    }
}