137. Single Number II

Given an array of integers, every element appears three times except for one, which appears exactly once. 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& nums) {
        int bits[32] = {0};
        for(int num : nums){
            int temp = num,index = 31;
            // while(temp){
            //     bits[index--] += temp & 1;
            //     temp = temp >> 1;
            // }
            for(int i = 0; i < 32; i ++){
                if(temp << i & (1 << 31))
                    bits[i] += 1;
            }
            
        }
        int num = 0;
        for(int i = 0; i < 32; i ++){
            bits[i] = bits[i] % 3;
            if(bits[i] != 0)
                num |= 1 << (31 - i);
        }
        return num;
    }
};