using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var dct = new Dictionary<string, string>();
		dct.Add("aa", "0");
		dct.Add("a1", "1");
		dct.Add("ab", "2");
		dct.Add("rr", "3");
		dct.Add("r0", "4");
		dct.Add("s0", "5");
		dct.Add("s1", "6");
		dct.Add("s2", "7");
		dct.Add("st", "8");
		dct.Add("ss", "9");
		dct.Add("lt", "10");
		dct.Add("ll", "11");
		var pat = $@"\b(?:{string.Join("|",dct.Keys.Select(k => Regex.Escape(k)).OrderByDescending(x => x.Length))})\b";
		Console.WriteLine(pat);
		var input ="aa a1 ab rr r0 s0 s1 s2 st ss lt ll lllllllrt";
		var output = Regex.Replace(input, pat, m => dct[m.Value]); 
		Console.Write(output);
	}
}
 

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