[C#][LeetCode][Easy] 535. Encode and Decode TinyURL

題目：

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.

心得：

這題實務上的話我應該會用資料庫來存key，簡單易用不是嗎？
不過要小心的是不能使用流水號來當作tinyurl的參數，
這樣會有被猜出key的可能性，可能就隨機產生一個短的字串並檢查不能重複來當key

我的答案(轉base64)：

public class Codec {

    // Encodes a URL to a shortened URL
    public string encode(string longUrl) {
        return Convert.ToBase64String(Encoding.UTF8.GetBytes(longUrl));
    }

    // Decodes a shortened URL to its original URL.
    public string decode(string shortUrl) {
        return Encoding.UTF8.GetString(Convert.FromBase64String(shortUrl));
    }
}

我的答案(guid)：

public class Codec {
    
    private static Dictionary<string, string> dty = new Dictionary<string, string>();
    
    // Encodes a URL to a shortened URL
    public string encode(string longUrl) {
        string guid = Guid.NewGuid().ToString();
        dty.Add(guid, longUrl);
        return guid;
    }

    // Decodes a shortened URL to its original URL.
    public string decode(string shortUrl) {
        string url = string.Empty;
        return dty.TryGetValue(shortUrl, out url) ? url : null;
    }
}