Valid Parentheses

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Problem

Given a string containing only the characters '(', ')', '{', '}', '[' and ']', determine whether the string is valid — every opening bracket must be closed by the same type of bracket, and brackets must close in the correct order.

Examples

Example 1

Input:s = "()[]{}"

Output:true

Example 2

Input:s = "(]"

Output:false

Constraints

1 <= s.length <= 10^4

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How to approach it: the Stack pattern

A stack is last-in-first-out — the most recently added item is the first one removed. It's the natural fit whenever "the most recent unmatched thing" matters, like nested brackets or undo history.

Look for this pattern when

You're validating nested or paired structures (parentheses, tags, nested expressions).
You need to track "the most recent X that hasn't been resolved yet."
You're looking for the next larger or smaller element relative to each position.

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Video walkthroughs

Original problem on LeetCode ↗