---
changelog:
  category: Release
  version: 20260827.192131.000000000
date: '2026-08-27T19:21:31Z'
seo:
  description: >-
    Finished Thu, Aug 27, 2026, 3:21 PM ET: all 3 core problems closed, 3
    problems closed that day. Scheduled: Thu Aug 27, 2026 · Phase: Phase I —
    Linear…
title: Topic 06 — Stack
type: changelog
---
<!-- release-topics: #8 -->
Finished Thu, Aug 27, 2026, 3:21 PM ET: all 3 core problems closed, 3 problems closed that day.

**Scheduled:** Thu Aug 27, 2026 · **Phase:** Phase I — Linear Structures · **Topic:** #8 · **Builds on:** independent primitive

## Closed Aug 27 — the day the topic finished

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #67 | LC 20 · Valid Parentheses | core | easy | Aug 27 | [py](https://github.com/prdlk/leetcode/blob/20260827.192131.000000000/work/Easy/String/20.valid-parentheses.py) · [docs](https://lc.prd.lk/20) |
| #68 | LC 155 · Min Stack | core | medium | Aug 27 | [py](https://github.com/prdlk/leetcode/blob/20260827.192131.000000000/work/Medium/Stack/155.min-stack.py) · [docs](https://lc.prd.lk/155) |
| #69 | LC 150 · Evaluate Reverse Polish Notation | core | medium | Aug 27 | [py](https://github.com/prdlk/leetcode/blob/20260827.192131.000000000/work/Medium/Array/150.evaluate-reverse-polish-notation.py) · [docs](https://lc.prd.lk/150) |

## Open at release

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #70 | LC 71 · Simplify Path | optional | medium | — | — |
| #71 | LC 224 · Basic Calculator | deferred | hard | — | — |

---

`20260827.192131.000000000` is [timever](https://gist.github.com/twolfson/de1b004dd22536b8e668) for the UTC instant the core set completed; it tags 9b5879b, the last main commit before it.