Single Number II

Question:

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?

Solution:

class Solution {
public:
    int singleNumber(vector<int>& nums) {
    sort(nums.begin(),nums.end());
    for(int i=0;i<nums.size();i+=3)
    {
        if(nums[i]!=nums[i+1])
        {
            return nums[i];
        }
    }    
    }
};