535. Encode and Decode TinyURL

Note: This is a companion problem to the System Design problem: Design TinyURL.
TinyURL is a URL shortening service where you enter a URL such as https://leetcode.com/problems/design-tinyurl and it returns a short URL such as http://tinyurl.com/4e9iAk.

Design the encode and decode methods for the TinyURL service. There is no restriction on how your encode/decode algorithm should work. You just need to ensure that a URL can be encoded to a tiny URL and the tiny URL can be decoded to the original URL.

class Solution {
    unordered_map<string, string> cache;
public:
    // Encodes a URL to a shortened URL.
    string encode(string longUrl) {
        string key = to_string(rand()%31) + to_string(time(0));
        cache[key] = longUrl;
        return key;
    }

    // Decodes a shortened URL to its original URL.
    string decode(string shortUrl) {
        return cache[shortUrl];
    }
};
// Your Solution object will be instantiated and called as such:
// Solution solution;
// solution.decode(solution.encode(url));