Initial data commit

Task/N-queens-problem/C-sharp/n-queens-problem-2.cs

@@ -0,0 +1,38 @@
+using System.Collections.Generic;
+using static System.Linq.Enumerable;
+using static System.Console;
+using static System.Math;
+
+namespace N_Queens
+{
+    static class Program
+    {
+        static void Main(string[] args)
+        {
+            var n = 8;
+            var cols = Range(0, n);
+            var solved = from v in cols.Permutations().Select(p => p.ToArray())
+                         where n == (from i in cols select v[i]+i).Distinct().Count()
+                         where n == (from i in cols select v[i]-i).Distinct().Count()
+                         select v;
+
+            WriteLine($"{n}-queens has {solved.Count()} solutions");
+            WriteLine("Position is row, value is column:-");
+            var first = string.Join(" ", solved.First());
+            WriteLine($"First Solution: {first}");
+            Read();
+        }
+
+        //Helpers from https://gist.github.com/martinfreedman/139dd0ec7df4737651482241e48b062f
+
+        public static IEnumerable<IEnumerable<T>> Permutations<T>(this IEnumerable<T> values)
+        {
+            if (values.Count() == 1)
+                return values.ToSingleton();
+
+            return values.SelectMany(v => Permutations(values.Except(v.ToSingleton())), (v, p) => p.Prepend(v));
+        }
+
+        public static IEnumerable<T> ToSingleton<T>(this T item) { yield return item; }
+    }
+}