Pattern-first LeetCode study notes by Steven Armenta. Algorithms, data structures, and the mental models behind them.https://stevenarmenta.dev/en-ushttps://stevenarmenta.dev/notes/20-valid-parentheses/https://stevenarmenta.dev/notes/20-valid-parentheses/A walkthrough of the classic stack-based approach to LeetCode 20, with the trigger-pattern-insight framing I use for every note.Fri, 01 May 2026 00:00:00 GMTStackEasystringstackhash-map