Refactor BinarySearchTree methods to use mutable lists instead of spread operators for improved performance in key retrieval.

Author: Ambaaq-Ajibike

DataStructures/BinarySearchTree/BinarySearchTree.cs

@@ -316,7 +316,12 @@ private IList<TKey> GetKeysInOrder(BinarySearchTreeNode<TKey>? node)
             return [];
         }
 
-        return [..GetKeysInOrder(node.Left), node.Key, ..GetKeysInOrder(node.Right)];
+        // Use mutable list approach instead of spread operator for better performance
+        var result = new List<TKey>();
+        result.AddRange(GetKeysInOrder(node.Left));
+        result.Add(node.Key);
+        result.AddRange(GetKeysInOrder(node.Right));
+        return result;
     }
 
     /// <summary>
@@ -331,7 +336,14 @@ private IList<TKey> GetKeysPreOrder(BinarySearchTreeNode<TKey>? node)
             return [];
         }
 
-        return [node.Key, ..GetKeysPreOrder(node.Left), ..GetKeysPreOrder(node.Right)];
+        // Use mutable list approach instead of spread operator for better performance
+        var result = new List<TKey>
+        {
+            node.Key,
+        };
+        result.AddRange(GetKeysPreOrder(node.Left));
+        result.AddRange(GetKeysPreOrder(node.Right));
+        return result;
     }
 
     /// <summary>
@@ -346,7 +358,12 @@ private IList<TKey> GetKeysPostOrder(BinarySearchTreeNode<TKey>? node)
             return [];
         }
 
-        return [..GetKeysPostOrder(node.Left), ..GetKeysPostOrder(node.Right), node.Key];
+        // Use mutable list approach instead of spread operator for better performance
+        var result = new List<TKey>();
+        result.AddRange(GetKeysPostOrder(node.Left));
+        result.AddRange(GetKeysPostOrder(node.Right));
+        result.Add(node.Key);
+        return result;
     }
 
     /// <summary>