Data update

Task/Determinant-and-permanent/C-sharp/determinant-and-permanent.cs

@@ -0,0 +1,89 @@
+using System;
+using System.Collections.Generic;
+using System.Linq; // This is required for LINQ extension methods
+
+class Program
+{
+    static IEnumerable<IEnumerable<int>> GetPermutations(IEnumerable<int> list, int length)
+    {
+        if (length == 1) return list.Select(t => new int[] { t });
+
+        return GetPermutations(list, length - 1)
+            .SelectMany(t => list.Where(e => !t.Contains(e)),
+                        (t1, t2) => t1.Concat(new int[] { t2 }));
+    }
+
+    static double Determinant(double[][] m)
+    {
+        double d = 0;
+        var p = new List<int>();
+        for (int i = 0; i < m.Length; i++)
+        {
+            p.Add(i);
+        }
+
+        var permutations = GetPermutations(p, p.Count);
+        foreach (var perm in permutations)
+        {
+            double pr = 1;
+            int sign = Math.Sign(GetPermutationSign(perm.ToList()));
+            for (int i = 0; i < perm.Count(); i++)
+            {
+                pr *= m[i][perm.ElementAt(i)];
+            }
+            d += sign * pr;
+        }
+
+        return d;
+    }
+
+    static int GetPermutationSign(IList<int> perm)
+    {
+        int inversions = 0;
+        for (int i = 0; i < perm.Count; i++)
+            for (int j = i + 1; j < perm.Count; j++)
+                if (perm[i] > perm[j])
+                    inversions++;
+        return inversions % 2 == 0 ? 1 : -1;
+    }
+
+    static double Permanent(double[][] m)
+    {
+        double d = 0;
+        var p = new List<int>();
+        for (int i = 0; i < m.Length; i++)
+        {
+            p.Add(i);
+        }
+
+        var permutations = GetPermutations(p, p.Count);
+        foreach (var perm in permutations)
+        {
+            double pr = 1;
+            for (int i = 0; i < perm.Count(); i++)
+            {
+                pr *= m[i][perm.ElementAt(i)];
+            }
+            d += pr;
+        }
+
+        return d;
+    }
+
+    static void Main(string[] args)
+    {
+        double[][] m2 = new double[][] {
+            new double[] { 1, 2 },
+            new double[] { 3, 4 }
+        };
+
+        double[][] m3 = new double[][] {
+            new double[] { 2, 9, 4 },
+            new double[] { 7, 5, 3 },
+            new double[] { 6, 1, 8 }
+        };
+
+        Console.WriteLine($"{Determinant(m2)}, {Permanent(m2)}");
+        Console.WriteLine($"{Determinant(m3)}, {Permanent(m3)}");
+    }
+}