Ducci.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace Ducci {
	static class DucciSolver {
		///<summary>
		///The entry point of the program
		///</summary>
		static void Main(string[] args) {
			//initial arguments
			List<int> arguments = ParseArguments(args);
			List<int> zeroes = ReturnZeroesList(arguments.Count);

			//the collection of lists
			List<List<int>> uberList = new List<List<int>> ();
			uberList.Add(arguments);

			//the process
			for (;;) {
				List<int> iterator = DucciProcess(uberList[uberList.Count - 1]);

				if (CheckAny(iterator, uberList) || CheckEqual(iterator, zeroes)) {
					uberList.Add(iterator);
					break;
				}
				
				//I don't like code duplication
				uberList.Add(iterator);
			} 

			//print the output
			foreach (List<int> list in uberList) {
				Console.WriteLine("[" + String.Join("; ", list) + "]");
			}
			Console.WriteLine(uberList.Count + " steps");
		}

		///<summary>
		///Parse each argument into an integer, throwing an exception on error
		///</summary>
		static List<int> ParseArguments(string[] args) {
			List<int> result = new List<int> ();
			foreach (string arg in args) {
				result.Add(int.Parse(arg));
			}
			return result;
		}

		///<summary>
		///Return a list filled with zeroes
		///</summary>
		static List<int> ReturnZeroesList(int count) {
			List<int> result = new List<int> ();
			for (int i = 0; i < count; i++) {
				result.Add(0);
			}
			return result;
		}

		///<summary>
		///Compare two lists, return true if they're identical
		///</summary>
		static bool CheckEqual<T>(IList<T> a, IList<T> b) {
			if (a == null || b == null)
				return (a == null && b == null);

			if (a.Count != b.Count)
				return false;

			return a.SequenceEqual(b);
		}

		///<summary>
		///Compare an iterator to an uber list, and return true if the iterator is within that uber list
		///</summary>
		static bool CheckAny(List<int> iterator, List<List<int>> uberList) {
			foreach (List<int> list in uberList) {
				if (CheckEqual(iterator, list)) {
					return true;
				}
			}
			return false;
		}

		///<summary>
		///Perform a single step of the Ducci Process
		///</summary>
		static List<int> DucciProcess(List<int> arg) {
			//the result
			List<int> result = new List<int>();

			//crunch each pair, not including the first and last
			for (int i = 1; i < arg.Count; i++) {
				result.Add(Math.Abs(arg[i] - arg[i-1]));
			}

			//crunch the first and last
			result.Add(Math.Abs(arg[0] - arg[arg.Count-1]));

			//finally
			return result;
		}
	}
}