---
changelog:
  category: Release
  version: 20260904.204425.000000000
date: '2026-09-04T20:44:25Z'
seo:
  description: >-
    Finished Fri, Sep 4, 2026, 4:44 PM ET: all 3 core problems closed, 3
    problems closed that day. Scheduled: Fri Sep 4, 2026 · Phase: Phase III —
    Hierarchical ·…
title: Topic 12 — Tree BFS
type: changelog
---
<!-- release-topics: #14 -->
Finished Fri, Sep 4, 2026, 4:44 PM ET: all 3 core problems closed, 3 problems closed that day.

**Scheduled:** Fri Sep 4, 2026 · **Phase:** Phase III — Hierarchical · **Topic:** #14 · **Builds on:** the queue primitive + Topic 11

## Closed Sep 4 — the day the topic finished

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #106 | LC 102 · Level Order Traversal | core | medium | Sep 4 | [py](https://github.com/prdlk/leetcode/blob/20260904.204425.000000000/work/1/Medium/Tree/102.binary-tree-level-order-traversal.py) · [docs](https://lc.prd.lk/102) |
| #107 | LC 199 · Right Side View | core | medium | Sep 4 | [py](https://github.com/prdlk/leetcode/blob/20260904.204425.000000000/work/1/Medium/Tree/199.binary-tree-right-side-view.py) · [docs](https://lc.prd.lk/199) |
| #108 | LC 1448 · Count Good Nodes | core | medium | Sep 4 | [py](https://github.com/prdlk/leetcode/blob/20260904.204425.000000000/work/1/Medium/Tree/1448.count-good-nodes-in-binary-tree.py) · [docs](https://lc.prd.lk/1448) |

## Open at release

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #109 | LC 103 · Zigzag Level Order | optional | medium | — | — |
| #110 | LC 637 · Average of Levels | optional | easy | — | — |

---

`20260904.204425.000000000` is [timever](https://gist.github.com/twolfson/de1b004dd22536b8e668) for the UTC instant the core set completed; it tags 987eb7a, the last main commit before it.