---
changelog:
  category: Release
  version: 20260921.165108.000000000
date: '2026-09-21T16:51:08Z'
seo:
  description: >-
    Finished Mon, Sep 21, 2026, 12:51 PM ET: all 2 core problems closed, 2
    problems closed that day. Scheduled: Mon Sep 21, 2026 · Phase: Phase III —
    Hierarchical…
title: Topic 15 — Trie
type: changelog
---
<!-- release-topics: #17 -->
Finished Mon, Sep 21, 2026, 12:51 PM ET: all 2 core problems closed, 2 problems closed that day.

**Scheduled:** Mon Sep 21, 2026 · **Phase:** Phase III — Hierarchical · **Topic:** #17 · **Builds on:** Topic 11

## Closed Sep 21 — the day the topic finished

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #127 | LC 208 · Implement Trie | core | medium | Sep 21 | [py](https://github.com/prdlk/leetcode/blob/20260921.165108.000000000/work/1/Medium/Hash%20Table/208.implement-trie-prefix-tree.py) · [docs](https://lc.prd.lk/208) |
| #128 | LC 211 · Add & Search Words | core | medium | Sep 21 | [py](https://github.com/prdlk/leetcode/blob/20260921.165108.000000000/work/1/Medium/String/211.design-add-and-search-words-data-structure.py) · [docs](https://lc.prd.lk/211) |

## Open at release

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #129 | LC 212 · Word Search II | deferred | hard | — | — |
| #214 | LC 648 · Replace Words | optional | medium | — | — |

---

`20260921.165108.000000000` is [timever](https://gist.github.com/twolfson/de1b004dd22536b8e668) for the UTC instant the core set completed; it tags 204e178, the last main commit before it.