CONCEPT BLOGS
Multi-phase guides with mental models, worked examples, diagrams, and real edge cases — the public form of Learnisim AI's conceptual learning. Read here; train it interactively in the app.
![Is "([)]" valid? Is "{[]}" valid? Is "(" valid? overview diagram](/blogs/valid-parentheses-explained-tracing-and/diagrams/hero.svg)
Learn how the stack data structure solves bracket matching. Trace strings like "([)]" and "{[]}" to understand LIFO ordering and nesting rules.
Learn how the sliding window pattern finds the shortest substring in ADOBECODEBANC that covers ABC, complete with pointer mechanics and frequency tracking.
Learn the sliding window and char-map mental model by tracing longest substring without repeating characters on 'pwwkew' and avoiding the 'abba' backward-left trap.
![Group ["eat","tea","tan","ate","nat","bat"] overview diagram](/blogs/group-anagrams-explained-grouping-eat-tea-tan/diagrams/hero.svg)
Learn how to group anagrams efficiently using hash maps by tracing the exact execution on ["eat","tea","tan","ate","nat","bat"].
