From 4d8d6e0797e707ef193eb276e6470d4cc47e8cb5 Mon Sep 17 00:00:00 2001
From: DeoJin <268571697+DeoJin@users.noreply.github.com>
Date: Tue, 17 Mar 2026 11:52:45 +0100
Subject: [PATCH] fix: preserve parent when replacing binary tree child

---
 src/data-structures/tree/BinaryTreeNode.js               | 4 ++--
 src/data-structures/tree/__test__/BinaryTreeNode.test.js | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/data-structures/tree/BinaryTreeNode.js b/src/data-structures/tree/BinaryTreeNode.js
index 44c9390e41..e8ff03aeee 100644
--- a/src/data-structures/tree/BinaryTreeNode.js
+++ b/src/data-structures/tree/BinaryTreeNode.js
@@ -166,12 +166,12 @@ export default class BinaryTreeNode {
     }
 
     if (this.left && this.nodeComparator.equal(this.left, nodeToReplace)) {
-      this.left = replacementNode;
+      this.setLeft(replacementNode);
       return true;
     }
 
     if (this.right && this.nodeComparator.equal(this.right, nodeToReplace)) {
-      this.right = replacementNode;
+      this.setRight(replacementNode);
       return true;
     }
 
diff --git a/src/data-structures/tree/__test__/BinaryTreeNode.test.js b/src/data-structures/tree/__test__/BinaryTreeNode.test.js
index 8eeda4dda5..3b5d485c6e 100644
--- a/src/data-structures/tree/__test__/BinaryTreeNode.test.js
+++ b/src/data-structures/tree/__test__/BinaryTreeNode.test.js
@@ -91,6 +91,7 @@ describe('BinaryTreeNode', () => {
 
     expect(rootNode.replaceChild(rootNode.right, rootNode.right.right)).toBe(true);
     expect(rootNode.right.value).toBe(5);
+    expect(rootNode.right.parent).toEqual(rootNode);
     expect(rootNode.right.right).toBeNull();
     expect(rootNode.traverseInOrder()).toEqual([1, 2, 5]);