Codewars kata

using System.Collections.Generic;
using System.Linq;
using System;
public class Kata
{
    public static List<string> GetPINs(string observed)
    {
        var result = new List<string>();
      var max = Convert.ToInt32(new String('9', observed.Length));
        var masks = Enumerable.Range(0, max + 1).Select(s => AddZeroes(s, observed.Length));
        foreach (string mask in masks)
        {
            try
            {
                var pin = "";

                for (int i = 0; i < observed.Length; i++)
                {
                    pin += GetAdjacent(observed[i])[mask[i] - '0'];
                }
                result.Add(pin);
            }
            catch
            {
                continue;
            }
        }
        return result;
    }

    private static string AddZeroes(int n, int length)
    {
        string result = n.ToString();
        result = new String('0', length - result.Length) + result;
        return result;
    }

    private static List<char> GetAdjacent(char digit)
    {
      if (digit == '0') return new List<char>() {'0', '8'};
      if (digit == '1') return new List<char>() {'1', '2', '4'};
      if (digit == '2') return new List<char>() {'1', '2', '3', '5'};
      if (digit == '3') return new List<char>() {'2', '3', '6'};
      if (digit == '4') return new List<char>() {'1', '4', '5', '7'};
      if (digit == '5') return new List<char>() {'2', '4', '5', '6', '8'};
      if (digit == '6') return new List<char>() {'3', '5', '6', '9'};
      if (digit == '7') return new List<char>() {'4', '7', '8'};
      if (digit == '8') return new List<char>() {'5', '7', '8', '9', '0'};
      if (digit == '9') return new List<char>() {'6', '8', '9'};
      throw new ArgumentOutOfRangeException();
    }


}