From 47a8f5f11235c80dd16bb0a6ac5fc7bd62f7f931 Mon Sep 17 00:00:00 2001
From: DeoJin <268571697+DeoJin@users.noreply.github.com>
Date: Tue, 17 Mar 2026 10:44:27 +0100
Subject: [PATCH] fix(tree): keep parent pointer when replacing children

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

diff --git a/src/data-structures/tree/BinaryTreeNode.js b/src/data-structures/tree/BinaryTreeNode.js
index 44c9390e41..ca0c27f3cf 100644
--- a/src/data-structures/tree/BinaryTreeNode.js
+++ b/src/data-structures/tree/BinaryTreeNode.js
@@ -167,11 +167,13 @@ export default class BinaryTreeNode {
 
     if (this.left && this.nodeComparator.equal(this.left, nodeToReplace)) {
       this.left = replacementNode;
+      this.left.parent = this;
       return true;
     }
 
     if (this.right && this.nodeComparator.equal(this.right, nodeToReplace)) {
       this.right = replacementNode;
+      this.right.parent = this;
       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]);