168. Excel表列名称

class Solution 
{
public:
    string convertToTitle(int n) 
    {
        unordered_map<int,char> hash;
        for(int i = 1;i <= 26;i ++) hash[i] = 'A' + i - 1;
        string res;
        while(n)
        {
            if(n % 26 == 0) n--,res = hash[n % 26 + 1] + res;
            else res = hash[n % 26] + res;
            n = n / 26;
        }
        return res;
    }
};