Query Mess

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

public class Program
{
    public static void Main()
    {
        const string pattern = @"([^&?]+?)=([^&?]+)";
        Regex whitespacePattern = new Regex(@"(%20|\+)+");

        string input = Console.ReadLine();

        while (input != "END")
        {
            var queries = new Dictionary<string, List<string>>();

            var matches = Regex.Matches(input, pattern);

            foreach (Match match in matches)
            {
                string key = match.Groups[1].ToString();
                key = whitespacePattern.Replace(key, " ").Trim();

                string value = match.Groups[2].ToString();
                value = whitespacePattern.Replace(value, " ").Trim();

                if (!queries.ContainsKey(key))
                {
                    queries.Add(key, new List<string>());
                }

                queries[key].Add(value);
            }

            foreach (var query in queries)
            {
                Console.Write(
                    "{0}=[{1}]",
                    query.Key,
                    string.Join(", ", query.Value));
            }

            Console.WriteLine();

            input = Console.ReadLine();
        }
    }
}