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 num=0, mask=1;
        int len = sizeof(int) * 8;
        unsigned int ans = 0,bit;
        for(int i=0;i<len;i++) {
            bit = 0;
            for(int j=0;j<n;j++) {
                if(A[j]&mask) bit++;
            }
            bit = bit%3;
            if(bit == 2) bit = bit/2;
            ans = ans|(bit<<i);
            mask = mask<<1;
        }
       num = ans;
        return num;
    }
};