code from 06.12.23 seminar

DigitalCathedral.Task2/CombinatoricsExtensions.cs

@@ -34,15 +34,49 @@ public static IEnumerable<IEnumerable<T>> GetAllPermutations<T>(
         IEqualityComparer<T> equalityComparer)
     {
         ThrowIfNotDistinctElements(values, equalityComparer);
-        throw new NotImplementedException();
+        var valuesArray = values.ToArray();
+
+        if (valuesArray.Length == 0)
+        {
+            yield return Enumerable.Empty<T>();
+            yield break;
+        }
+
+        foreach (var permutation in GetAllPermutations(new List<T>(valuesArray.Length), valuesArray.ToList()))
+        {
+            yield return permutation;
+        }
+    }
+
+    private static IEnumerable<IEnumerable<T>> GetAllPermutations<T>(
+        List<T> wereAdded,
+        List<T> notAdded)
+    {
+        if (notAdded.Count == 0)
+        {
+            yield return wereAdded.ToList();
+        }
+
+        for (var i = 0; i < notAdded.Count; i++)
+        {
+            wereAdded.Add(notAdded[i]);
+            notAdded.RemoveAt(i);
+
+            foreach (var permutation in GetAllPermutations(wereAdded, notAdded))
+            {
+                yield return permutation;
+            }
+
+            notAdded.Insert(i, wereAdded.Last());
+            wereAdded.RemoveAt(wereAdded.Count - 1);
+        }
     }
 
     private static void ThrowIfNotDistinctElements<T>(
         IEnumerable<T> values,
         IEqualityComparer<T> equalityComparer)
     {
-        var distinctValues = values.Distinct(equalityComparer).ToArray();
-        if (distinctValues.Length != values.Count())
+        if (values.Distinct(equalityComparer).Count() != values.Count())
         {
             throw new ArgumentException("Found equal elements in  collection.", nameof(values));
         }

DigitalCathedral.Task2/IEnumerableImpl.cs

@@ -0,0 +1,24 @@
+using System.Collections;
+
+namespace DigitalCathedral.Task2;
+
+public class IEnumerableImpl:
+    IEnumerable<int>
+{
+
+    private readonly int[] _values = new[] { 1, 2, 3, 7, 5 };
+
+    IEnumerator IEnumerable.GetEnumerator()
+    {
+        return _values.GetEnumerator();
+    }
+
+    public IEnumerator<int> GetEnumerator()
+    {
+        for (var i = 0; i < _values.Length; i++)
+        {
+            yield return _values[i];
+        }
+    }
+
+}

DigitalCathedral.Task2/Program.cs

@@ -3,8 +3,18 @@
 try
 {
     IEqualityComparer<int> equalityComparer = new IntEqualityComparer();
-    var values = new int [] { 1, 2, 3, 4, 5 };
-    values.GetCombinations(3, equalityComparer);
+    var i = 0;
+    foreach (var permutation in new IEnumerableImpl().Prepend(8).Append(15).GetAllPermutations(EqualityComparer<int>.Default).Take(1000))
+    {
+        // Console.Write("[ ");
+        // foreach (var permutationComponent in permutation)
+        // {
+        //     Console.Write($"{permutationComponent} ");
+        // }
+        // Console.WriteLine("]");
+
+        Console.WriteLine($"{++i}: [ {string.Join(" ", permutation)} ]");
+    }
 }
 catch (ArgumentException ex)
 {

DigitalCathedral/Program.cs

@@ -291,9 +291,20 @@
     Console.WriteLine((int)iterator.Current);
 }
 
-(impl as IEnumerable<int>).
+var iterator2 = ((IEnumerable<int>)impl).GetEnumerator();
+while (iterator2.MoveNext())
+{
+    var value = iterator2.Current;
+    if (value == 2)
+    {
+        break;
+    }
+    Console.WriteLine(iterator2.Current);
+}
+
+//(impl as IEnumerable<int>).
 
-Enumerable.Cast<int>(impl);
+//Enumerable.Cast<int>(impl);
 
 void Foo2(int value1, string value2)
 {
@@ -348,7 +359,7 @@ double IntegrandFunc(double value)
 Integral integral = null;
 integral += (f, bounds, eps) =>
 {
-
+    throw new NotImplementedException();
 };
 integral?.Invoke(IntegrandFunc, (5.0, 10.0), 0.0001);