Leetcode 137: Single Number II

Given an array of integers, every element appears three times except for one, which appears exactly once. 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[] nums) {
        int result = 0, bitMask = 0x1;
        
        for (int i = 0; i < 32; i++)
        {
            int count = 0;
            for (int j = 0; j < nums.Length; j++)
            {
                int d = nums[j] & bitMask;
                if (d != 0) count++;
            }
            
            if (count % 3 != 0)
            {
                result |= bitMask;
            }
            
            bitMask <<= 1;
        }
        
        return result;
    }
}