Refactor Permutations in EnumerableExtensions, add PermutationsWithRepeats method, and update tests for improved validation and clarity

AdventOfCode.Extensions/EnumerableExtensions.cs

@@ -68,7 +68,7 @@ public static class EnumerableExtensions
         }
     }
     
-    public static IEnumerable<TValue[]> Permutations<TValue>(this IEnumerable<TValue> values, int count)
+    public static IEnumerable<TValue[]> PermutationsWithRepeats<TValue>(this IEnumerable<TValue> values, int count)
     {
         var pool = values.ToArray();
         if (count > pool.Length)
@@ -96,6 +96,47 @@ public static class EnumerableExtensions
         }
     }
     
+    public static IEnumerable<TValue[]> Permutations<TValue>(this IEnumerable<TValue> values, int count)
+    {
+        var pool = values.ToArray();
+        var poolLength = pool.Length;
+        if (count > poolLength)
+            yield break;
+        var indices = Enumerable.Range(0, poolLength).ToArray();
+        var cycles = Enumerable.Range(0, poolLength + 1)
+            .Skip(poolLength - count + 1)
+            .Reverse()
+            .ToArray();
+        yield return GetCombination(indices[..count], pool);
+        var notDone = true;
+        while (notDone)
+        {
+            notDone = false;
+            for (var i = count - 1; i >= 0; i--)
+            {
+                cycles[i] -= 1;
+                if (cycles[i] == 0)
+                {
+                    var tmp = indices[i];
+                    for (var j = i; j < indices.Length - 1; j++)
+                    {
+                        indices[j] = indices[j + 1];
+                    }
+                    indices[^1] = tmp;
+                    cycles[i] = poolLength - i;
+                }
+                else
+                {
+                    var j = cycles[i];
+                    (indices[i], indices[^j]) = (indices[^j], indices[i]);
+                    yield return GetCombination(indices[..count], pool);
+                    notDone = true;
+                    break;
+                }
+            }
+        }
+    }
+    
     private static TValue[] GetCombination<TValue>(int[] innerIndices, TValue[] innerPool) => 
         innerIndices.Select(i => innerPool[i]).ToArray();
 }