🎉 Release v1.2.0: Problem System Unification & Site Hardening

This release unifies the problem-tracking infrastructure across all DSA topic pages, redesigns the problem card system, fixes long-standing UI bugs, and delivers a full documentation refresh.

🚀 Major Features & Updates

1. Unified Problem Card System

Canonical _includes/problem-card.html component: Replaced all per-topic hardcoded HTML cards with a single reusable Liquid include. Every topic page now renders identical, consistent cards driven directly from _data/problems.yml.
New .pc-card CSS system: Introduced .pc-card, .pc-card--easy/medium/hard, .pc-status, .pc-diff, .pc-btn, .pc-grid classes in main.css. Cards use CSS custom properties for seamless dark/light mode compatibility — no more visibility issues in dark theme.
Single source of truth: _data/problems.yml now drives both the Interactive Problems Hub (/problems/) and all six dedicated topic pages simultaneously. Adding one YAML entry propagates everywhere automatically.

2. Liquid-Powered Topic Pages (All 6)

Replaced all old hardcoded HTML problem lists with clean Liquid templates using Jekyll’s where_exp filter:

/learning/dsa/arrays/arrays-problems/
/learning/dsa/strings/strings-problems/
/learning/dsa/linked-list/linked-list-problems/
/learning/dsa/tree/tree-problems/
/learning/dsa/stacks/stacks-problems/
/learning/dsa/searching-sorting/searching-sorting-problems/

Each page shows live stats (Total / Solved / Easy / Medium / Hard) and groups problems by difficulty using the canonical card component.

Topic chips row on the Problems Hub for one-click jumps to dedicated topic pages.
Topic page banner in the hub: when filtering by a topic that has a dedicated page, a banner appears linking directly to it.
Clickable topic tags in the hub table: tags with dedicated pages link to them; tags without pages trigger an inline filter.
Back-to-top link on long problem lists.
Cross-links on every topic page: All Problems Hub ↔ Back to Topic ↔ DSA Hub.

4. Dark Mode Fix

Added synchronous <script> in <head> to apply the saved theme before first paint — eliminates flash of unstyled content (FOUC).
Extracted theme toggle into an isolated IIFE at end of <body>, fully decoupled from SimpleJekyllSearch’s DOMContentLoaded handler which was silently blocking the click listener on error.

5. DSA Hub Card Redesign

Reduced padding and font sizes; switched to horizontal flex layout.
Stats row changed from grid to flex for a more compact, readable presentation.

6. Repository Cleanup

Removed arrays_backup/: Confirmed identical duplicate of _learning/dsa/Arrays/ — deleted entirely with zero data loss.
Suppressed sorting/ stubs: All five stub pages (index, mergesort, quicksort, heapsort, counting-radix-bucket) marked published: false. Their content was already fully covered by Searching-Sorting/sorting-guide.md.
Fixed dead link in DSA hub: master-problem-list/ (non-existent) replaced with the live /problems/ hub.
Resolved permalink conflict: arrays_backup/ was serving the same URL as Arrays/arrays-problems.md, causing Jekyll to overwrite the new page with the old backup on every build. Fixed by suppressing the backup before deletion.

7. Problems Data Updates

Added LeetCode 88 (Merge Sorted Array — easy, searching-sorting + arrays + two-pointers, solved) which was present in sorting-guide.md but missing from problems.yml.
Filled solution URLs for problems 148 (Sort List), 179 (Largest Number), and 75 (Sort Colors) — all had published LeetCode solutions but empty solution_url fields.

8. Documentation Refresh

README.md — complete rewrite aligned to the current codebase: accurate quick-start, Problems system data-flow diagram, topic slug reference, DSA topic page template, updated file map, deploy workflow, and common mistakes table.
EDITORIALS_GUIDE.md — expanded from a short CMS reference into a full developer guide covering: problems.yml schema, all 5 solution attachment options (editorial MD, PDF, raw code, LeetCode link, CMS UI), approach_url vs solution_url rules, step-by-step new topic page creation, and a troubleshooting table.

Compiled on: February 28, 2026