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?

class Solution {public:    int singleNumber(int A[], int n)    {        int res = 0;        for (int i = 0; i < 32; i++)        {            int val = 0;            for (int j = 0; j < n; j++)            {                val += (A[j] >> i & 1);            }            val = val % 3;            if (1 == val)                res |= 1<<i;        }        return res;    }};