leetcode: 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 result = 0;
for (int i=0; i<32; i++)
{
int curSum = 0;
for (int idx=0; idx<n; idx++)
{
if (A[idx] & (1<<i))
{
curSum++;
}
}

if (curSum%3)
{
result |= 1<<i;
}
}
return result;
}
};