using System;

using System.Collections.Generic;

public class Program

{   

    public static void Main()

    {

        string tiny1 = Codec.encode("https://leetcode.com/problems/design-tinyurl-1");

        string tiny2 = Codec.encode("https://leetcode.com/problems/design-tinyurl-2");

        Console.WriteLine(Codec.decode(tiny1) + " - " + tiny1);

        Console.WriteLine(Codec.decode(tiny2) + " - " + tiny2);

    }

}

​

public static class Codec {

    static char[] map = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',

                  'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',

                  '0','1','2','3','4','5','6','7','8','9'};

    static int ID = 0; //auto-increment

    static Dictionary<string,string> memStore = new Dictionary<string,string>(); //stores id to original URL mapping    

    // Encodes a URL to a shortened URL

    public static string encode(string longUrl) {

        string shortUrl = string.Empty;

        int val = ID;

        if(val == 0){

            shortUrl += map[0];

        }else{      

            while(val > 0){

                shortUrl += map[val % 62];

                val /= 62;

            }

        }

        shortUrl = Reverse(shortUrl);

        memStore.Add(shortUrl,longUrl);

        ID++;   //increment ID for next one

        return shortUrl;

    }

​

    // Decodes a shortened URL to its original URL.

    public static string decode(string shortUrl) {

        return memStore[shortUrl];

    }

    public static string Reverse( string s )

    {

        char[] charArray = s.ToCharArray();

        Array.Reverse( charArray );

        return new string( charArray );

    }

}