[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?

Analysis:

Count the numbers of each bit for all integers and the bit which is not times of 3 is the bit of the integer appears once.

class Solution {
public:
    int singleNumber(int A[], int n) {
        vector<int> nums(32,0);
        for(int i=0; i<n; i++)
        {
            int num = A[i];
            for(int j=0; j<32;j++)
            {
                nums[j] += (num >> j) & 0x1;
            }
        }
        
        int ret = 0;
        for(int i=0; i<32;i++)
        {
            if (nums[i] % 3)
                ret = ret | (0x1 << i);
        }       
        
        return ret;
    }
};