---
changelog:
  category: Release
  version: 20260903.181810.000000000
date: '2026-09-03T18:18:10Z'
seo:
  description: >-
    Finished Thu, Sep 3, 2026, 2:18 PM ET: all 3 core problems closed, 3
    problems closed that day. Scheduled: Thu Sep 3, 2026 · Phase: Phase III —
    Hierarchical ·…
title: Topic 11 — Tree DFS
type: changelog
---
<!-- release-topics: #13 -->
Finished Thu, Sep 3, 2026, 2:18 PM ET: all 3 core problems closed, 3 problems closed that day.

**Scheduled:** Thu Sep 3, 2026 · **Phase:** Phase III — Hierarchical · **Topic:** #13 · **Builds on:** recursion

## Closed Sep 3 — the day the topic finished

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #96 | LC 226 · Invert Binary Tree | core | easy | Sep 3 | [py](https://github.com/prdlk/leetcode/blob/20260903.181810.000000000/work/1/Easy/Tree/226.invert-binary-tree.py) · [docs](https://lc.prd.lk/226) |
| #97 | LC 104 · Maximum Depth of Binary Tree | core | easy | Sep 3 | [py](https://github.com/prdlk/leetcode/blob/20260903.181810.000000000/work/1/Easy/Tree/104.maximum-depth-of-binary-tree.py) · [docs](https://lc.prd.lk/104) |
| #98 | LC 236 · Lowest Common Ancestor | core | medium | Sep 3 | [py](https://github.com/prdlk/leetcode/blob/20260903.181810.000000000/work/1/Medium/Tree/236.lowest-common-ancestor-of-a-binary-tree.py) · [docs](https://lc.prd.lk/236) |

## Open at release

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #99 | LC 100 · Same Tree | optional | easy | — | — |
| #100 | LC 572 · Subtree of Another Tree | optional | easy | — | — |
| #101 | LC 101 · Symmetric Tree | optional | easy | — | — |
| #102 | LC 112 · Path Sum | optional | easy | — | — |
| #103 | LC 129 · Sum Root to Leaf Numbers | optional | medium | — | — |
| #104 | LC 543 · Diameter of Binary Tree | optional | easy | — | — |
| #105 | LC 124 · Binary Tree Maximum Path Sum | deferred | hard | — | — |

---

`20260903.181810.000000000` is [timever](https://gist.github.com/twolfson/de1b004dd22536b8e668) for the UTC instant the core set completed; it tags 9008251, the last main commit before it.