Encode and Decode TinyURL.cpp

class Solution {
public:
    
    // Encodes a URL to a shortened URL.
    string encode(string longUrl) {
        int base = 62, id = _id++;
        string res = "";
        while(id)
        {
            int digit = id % base;
            res = _s[digit] + res;
            id /= base;
        }
        if(res.size() < 6)res = string(6 - res.size(), '0') + res;
        _s2l[res] = longUrl;
        return res;
    }

    // Decodes a shortened URL to its original URL.
    string decode(string shortUrl) {
        return _s2l[shortUrl];
    }

private:
    int _id = 0;
    string _s = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    unordered_map<string, string> _s2l;
    
};

// Your Solution object will be instantiated and called as such:
// Solution solution;
// solution.decode(solution.encode(url));