LeetCode 20: Valid Parentheses (Amazon & Google) | DSA Stack Series | AlgoXploration

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In this video, we learn how to check whether a string of parentheses is valid using the stack data structure — one of the most common and fundamental interview problems. A string is considered valid when every opening bracket has a corresponding closing bracket in the correct order.

What this video covers
How to use a stack to track opening brackets
Matching parentheses: (), {}, []
Why checking order matters
Step-by-step explanation of push/pop operations
Edge cases:
Extra closing brackets
Unmatched opening brackets
Mixed types of brackets
How to return true/false based on stack state

Time Complexity: O(n)
Space Complexity: O(n)

Why this matters
This is one of the most frequently asked stack problems in coding interviews. Understanding this pattern builds the foundation for more advanced problems like expression evaluation, infix-to-postfix conversion, and parsing logic.

Timeline


Understanding the problem
How a stack helps
Step-by-step dry run
Returning final answer

Practice Question
LeetCode – Valid Parentheses
https://leetcode.com/problems/valid-p...
Other Related Problems:
https://leetcode.com/problems/minimum...
https://leetcode.com/problems/minimum...
(Optional) https://leetcode.com/problems/longest...

Code
👉 Solution: Pinned on the comments

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