leetcode——137—— 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(vector<int>& nums) {
        int length = nums.size();  
        int result = 0;  
        for(int i = 0; i<32; i++){  
            int count = 0;   
            int mask = 1<< i;  
            for(int j=0; j<length; j++){  
                if(nums[j] & mask)  
                    count++;  
            }  
          if(count %3)  
                result |= mask;  
        }  
        return result; 

    }
};