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) {

        const int LENGTH=32;

        

        int dig[LENGTH];

        for(int i=0;i<LENGTH;i++)

            dig[i]=0;

        

        for(int i=0;i<n;i++)

        {

            unsigned num=A[i];

            for(int j=0;j<LENGTH && num!=0;j++)

            {

                if(num & 0x1==1)

                {

                    dig[j]++;

                    if(dig[j]==3) dig[j]=0;

                }

                num=(num>>1);

            }

        }

        

        unsigned num=0;

        for(int i=0;i<LENGTH;i++)

        {

            num=(dig[i]<<i)+num;

        }

        return num;

    }

};