Data commit

Task/Hofstadter-Q-sequence/C-sharp/hofstadter-q-sequence.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Collections.Generic;
+
+namespace HofstadterQSequence
+{
+    class Program
+    {
+        // Initialize the dictionary with the first two indices filled.
+        private static readonly Dictionary<int, int> QList = new Dictionary<int, int>
+                                                                 {
+                                                                     {1, 1},
+                                                                     {2, 1}
+                                                                 };
+
+        private static void Main()
+        {
+            int lessThanLast = 0;
+                /* Initialize our variable that holds the number of times
+                                   * a member of the sequence was less than its preceding term. */
+
+            for (int n = 1; n <= 100000; n++)
+            {
+                int q = Q(n); // Get Q(n).
+
+                if (n > 1 && QList[n - 1] > q) // If Q(n) is less than Q(n - 1),
+                    lessThanLast++;            // then add to the counter.
+
+                if (n > 10 && n != 1000) continue; /* If n is greater than 10 and not 1000,
+                                                    * the rest of the code in the loop does not apply,
+                                                    * and it will be skipped. */
+
+                if (!Confirm(n, q)) // Confirm Q(n) is correct.
+                    throw new Exception(string.Format("Invalid result: Q({0}) != {1}", n, q));
+
+                Console.WriteLine("Q({0}) = {1}", n, q); // Write Q(n) to the console.
+            }
+
+            Console.WriteLine("Number of times a member of the sequence was less than its preceding term: {0}.",
+                              lessThanLast);
+        }
+
+        private static bool Confirm(int n, int value)
+        {
+            if (n <= 10)
+                return new[] {1, 1, 2, 3, 3, 4, 5, 5, 6, 6}[n - 1] == value;
+            if (n == 1000)
+                return 502 == value;
+            throw new ArgumentException("Invalid index.", "n");
+        }
+
+        private static int Q(int n)
+        {
+            int q;
+
+            if (!QList.TryGetValue(n, out q)) // Try to get Q(n) from the dictionary.
+            {
+                q = Q(n - Q(n - 1)) + Q(n - Q(n - 2)); // If it's not available, then calculate it.
+                QList.Add(n, q); // Add it to the dictionary.
+            }
+
+            return q;
+        }
+    }
+}