---
changelog:
  category: Release
  version: 20260825.190101.000000000
date: '2026-08-25T19:01:01Z'
seo:
  description: >-
    Finished Tue, Aug 25, 2026, 3:01 PM ET: all 4 core problems closed, 3
    problems closed that day. Scheduled: Tue Aug 25, 2026 · Phase: Phase I —
    Linear…
title: Topic 04 — Sliding Window
type: changelog
---
<!-- release-topics: #6 -->
Finished Tue, Aug 25, 2026, 3:01 PM ET: all 4 core problems closed, 3 problems closed that day.

**Scheduled:** Tue Aug 25, 2026 · **Phase:** Phase I — Linear Structures · **Topic:** #6 · **Builds on:** Topic 3

## Closed Aug 25 — the day the topic finished

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #51 | LC 3 · Longest Substring Without Repeating Characters | core | medium | Aug 25 | [py](https://github.com/prdlk/leetcode/blob/20260825.190101.000000000/work/Medium/Hash%20Table/3.longest-substring-without-repeating-characters.py) · [docs](https://lc.prd.lk/3) |
| #52 | LC 424 · Longest Repeating Character Replacement | core | medium | Aug 25 | [py](https://github.com/prdlk/leetcode/blob/20260825.190101.000000000/work/Medium/Hash%20Table/424.longest-repeating-character-replacement.py) · [docs](https://lc.prd.lk/424) |
| #53 | LC 567 · Permutation in String | core | medium | Aug 25 | [py](https://github.com/prdlk/leetcode/blob/20260825.190101.000000000/work/Medium/Hash%20Table/567.permutation-in-string.py) · [docs](https://lc.prd.lk/567) |

## Closed earlier

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #50 | LC 121 · Best Time to Buy and Sell Stock | core | easy | Aug 24 | [py](https://github.com/prdlk/leetcode/blob/20260825.190101.000000000/work/Easy/Array/121.best-time-to-buy-and-sell-stock.py) · [docs](https://lc.prd.lk/121) |

## Open at release

| Issue | Problem | Set | Difficulty | Closed (ET) | Solution |
| --- | --- | --- | --- | --- | --- |
| #54 | LC 209 · Minimum Size Subarray Sum | optional | medium | — | — |
| #55 | LC 643 · Maximum Average Subarray | optional | easy | — | — |
| #56 | LC 1004 · Max Consecutive Ones III | optional | medium | — | — |
| #57 | LC 76 · Minimum Window Substring | deferred | hard | — | — |

---

`20260825.190101.000000000` is [timever](https://gist.github.com/twolfson/de1b004dd22536b8e668) for the UTC instant the core set completed; it tags aba3d9b, the last main commit before it.