Data commit

Task/Hofstadter-Figure-Figure-sequences/C-sharp/hofstadter-figure-figure-sequences.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace HofstadterFigureFigure
+{
+	class HofstadterFigureFigure
+	{
+		readonly List<int> _r = new List<int>() {1};
+		readonly List<int> _s = new List<int>();
+
+		public IEnumerable<int> R()
+		{
+			int iR = 0;
+			while (true)
+			{
+				if (iR >= _r.Count)
+				{
+					Advance();
+				}
+				yield return _r[iR++];
+			}
+		}
+
+		public IEnumerable<int> S()
+		{
+			int iS = 0;
+			while (true)
+			{
+				if (iS >= _s.Count)
+				{
+					Advance();
+				}
+				yield return _s[iS++];
+			}
+		}
+
+		private void Advance()
+		{
+			int rCount = _r.Count;
+			int oldR = _r[rCount - 1];
+			int sVal;
+			
+			// Take care of first two cases specially since S won't be larger than R at that point
+			switch (rCount)
+			{
+				case 1:
+					sVal = 2;
+					break;
+				case 2:
+					sVal = 4;
+					break;
+				default:
+					sVal = _s[rCount - 1];
+					break;
+			}
+			_r.Add(_r[rCount - 1] + sVal);
+			int newR = _r[rCount];
+			for (int iS = oldR + 1; iS < newR; iS++)
+			{
+				_s.Add(iS);
+			}
+		}
+	}
+
+	class Program
+	{
+		static void Main()
+		{
+			var hff = new HofstadterFigureFigure();
+			var rs = hff.R();
+			var arr = rs.Take(40).ToList();
+
+			foreach(var v in arr.Take(10))
+			{
+				Console.WriteLine("{0}", v);
+			}
+
+			var hs = new HashSet<int>(arr);
+			hs.UnionWith(hff.S().Take(960));
+			Console.WriteLine(hs.Count == 1000 ? "Verified" : "Oops!  Something's wrong!");
+		}
+	}
+}