taras-labiak-test-task.cs

using System;

namespace Program
{
    public class Program
    {
        public const string Impossible = "IMPOSSIBLE";
        public const string StringEquals = "EQUALS";
        public const string Insert = "INSERT {0}";
        public const string Replace = "REPLACE {0} {1}";
        public const string Swap = "SWAP {0} {1}";

        public static int Main(string[] args)
        {
            Console.WriteLine("Taras Labiak test task (https://kissarat.github.io/). Please enter two words splitted by space");
            while(true) {
                var output = Console.ReadLine();
                if (0 == output.Length) {
                    break;
                }
                var parts = output.Trim().Split(' ');
                if (parts.Length != 2) {
                    Console.WriteLine("Invalid number of arguments");
                    continue;
                }
                Console.WriteLine(Compare(parts[0], parts[1]));
            }
			return 0;
        }

        public static string Compare(string first, string second) {
            if (first.Equals(second)) {
                return StringEquals;
            }
            var possiblyInsert = second.Length == first.Length + 1;
            var last = first.Length - 1;
            if (!(second.Length == first.Length || possiblyInsert)) {
                return Impossible;
            }
            for(int i = 0; i < first.Length; i++) {
                if (possiblyInsert) {
                    if (first.Substring(i).Equals(second.Substring(i+1))) {
                        return String.Format(Insert, second[i]);
                    }
                }
                if (first[i] == second[i]) {
                    continue;
                }
                if (first.Substring(i+1).Equals(second.Substring(i+1))) {
                    return String.Format(Replace, first[i], second[i]);
                }
                if (i < last) {
                    if (first[i] == second[i + 1] && first[i + 1] == second[i]) {
                        if (first.Substring(i+2).Equals(second.Substring(i+2))) {
                            return String.Format(Swap, first[i], first[i + 1]);
                        }
                    }
                }
                return Impossible;
            }
            return StringEquals;
        }
    }
}