Simplify Mastermind (C#) folder structure

60_Mastermind/csharp/EnumerableExtensions.cs

@@ -0,0 +1,88 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Game
+{
+    /// <summary>
+    /// Provides additional methods for the <see cref="IEnumerable{T}"/>
+    /// interface.
+    /// </summary>
+    public static class EnumerableExtensions
+    {
+        /// <summary>
+        /// Cycles through the integer values in the range [0, count).
+        /// </summary>
+        /// <param name="start">
+        /// The first value to return.
+        /// </param>
+        /// <param name="count">
+        /// The number of values to return.
+        /// </param>
+        public static IEnumerable<int> Cycle(int start, int count)
+        {
+            if (count < 1)
+                throw new ArgumentException("count must be at least 1");
+
+            if (start < 0 || start >= count)
+                throw new ArgumentException("start must be in the range [0, count)");
+
+            for (var i = start; i < count; ++i)
+                yield return i;
+
+            for (var i = 0; i < start; ++i)
+                yield return i;
+        }
+
+        /// <summary>
+        /// Finds the index of the first item in the given sequence that
+        /// satisfies the given predicate.
+        /// </summary>
+        /// <typeparam name="T">
+        /// The type of elements in the sequence.
+        /// </typeparam>
+        /// <param name="source">
+        /// The source sequence.
+        /// </param>
+        /// <param name="predicate">
+        /// The predicate function.
+        /// </param>
+        /// <returns>
+        /// The index of the first element in the source sequence for which
+        /// predicate(element) is true.  If there is no such element, return
+        /// is null.
+        /// </returns>
+        public static int? FindFirstIndex<T>(this IEnumerable<T> source, Func<T, bool> predicate) =>
+            source.Select((element, index) => predicate(element) ? index : default(int?))
+                .FirstOrDefault(index => index.HasValue);
+
+        /// <summary>
+        /// Returns the first item in the given sequence that matches the
+        /// given predicate.
+        /// </summary>
+        /// <typeparam name="T">
+        /// The type of elements in the sequence.
+        /// </typeparam>
+        /// <param name="source">
+        /// The source sequence.
+        /// </param>
+        /// <param name="predicate">
+        /// The predicate to check against each element.
+        /// </param>
+        /// <param name="defaultValue">
+        /// The value to return if no elements match the predicate.
+        /// </param>
+        /// <returns>
+        /// The first item in the source sequence that matches the given
+        /// predicate, or the provided default value if none do.
+        /// </returns>
+        public static T FirstOrDefault<T>(this IEnumerable<T> source, Func<T, bool> predicate, T defaultValue)
+        {
+            foreach (var element in source)
+                if (predicate(element))
+                    return element;
+
+            return defaultValue;
+        }
+    }
+}