[pull] master from williamfiset:master

.gemini.md

@@ -47,6 +47,11 @@ java -cp classes com.williamfiset.algorithms.<package>.<ClassName>
 
 ## Development Conventions
 
+### Documentation and Comments
+- **Educational Context:** This repository is an educational project. Most comments (except for the most trivial ones) must be preserved during refactoring.
+- **Purpose:** Comments should explain *how* and *why* an algorithm or data structure works to aid understanding for students and developers.
+- **Refactoring:** When simplifying code, ensure that the conceptual explanations remain intact.
+
 ### Project Structure
 - `src/main/java/com/williamfiset/algorithms/`: Implementation source code.
 - `src/test/java/com/williamfiset/algorithms/`: Unit tests (mirrors source structure).

src/main/java/com/williamfiset/algorithms/datastructures/balancedtree/AVLTreeRecursive.java

@@ -71,6 +71,7 @@ public boolean isEmpty() {
 
   // Return true/false depending on whether a value exists in the tree.
   public boolean contains(T value) {
+    if (value == null) return false;
     return contains(root, value);
   }
 
@@ -299,12 +300,12 @@ private T findMax(Node node) {
     return node.value;
   }
 
-  // Returns as iterator to traverse the tree in order.
+  // Returns an iterator to traverse the tree in order.
   public java.util.Iterator<T> iterator() {
 
     final int expectedNodeCount = nodeCount;
-    final java.util.Stack<Node> stack = new java.util.Stack<>();
-    stack.push(root);
+    final java.util.Deque<Node> stack = new java.util.ArrayDeque<>();
+    if (root != null) stack.push(root);
 
     return new java.util.Iterator<T>() {
       Node trav = root;
@@ -350,12 +351,12 @@ public String toString() {
   // Make sure all left child nodes are smaller in value than their parent and
   // make sure all right child nodes are greater in value than their parent.
   // (Used only for testing)
-  public boolean validateBSTInvarient(Node node) {
+  public boolean validateBSTInvariant(Node node) {
     if (node == null) return true;
     T val = node.value;
     boolean isValid = true;
     if (node.left != null) isValid = isValid && node.left.value.compareTo(val) < 0;
     if (node.right != null) isValid = isValid && node.right.value.compareTo(val) > 0;
-    return isValid && validateBSTInvarient(node.left) && validateBSTInvarient(node.right);
+    return isValid && validateBSTInvariant(node.left) && validateBSTInvariant(node.right);
   }
 }