Valid Parentheses Leetcode 20 - Stack Solution, O(n). #lindorcodes #dsa

LeetCode 20 Valid Parentheses is a classic stack problem that shows up in every FAANG loop. We walk through building a closing-to-opening dictionary, handling the empty stack edge case before every pop, and why returning `len(stack) == 0` at the end cleanly handles the all-open-brackets trap. Full whiteboard walkthrough, live LeetCode submission, and a clear breakdown of O(n) time and O(n) space — with emphasis on the one complexity mistake that trips people up mid-interview. If you're prepping for the Q4 2026 Google/FAANG cycle, this one's foundational.

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