Single Number II <LeetCode>

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?

 1 class Solution {
 2 public:
 3     int singleNumber(int A[], int n) {
 4         if(n==1)  return A[0];
 5         sort(A,A+n);
 6         int i=0;
 7         while(A[i]==A[i+2]&&1!=n-1)
 8         {
 9             i=i+3;
10         }
11         return A[i];
12     }
13 };