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Framework Thinking - Neetcode 150 - Valid Parentheses

Here is the problem for Valid Parentheses.

1. Understand the problem

Given a string s containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’, and ‘]’, determine if the input string is valid. A string is valid if:

Open brackets are closed by the same type of brackets.
Open brackets are closed in the correct order.

2. Clarify requirements

Only contains ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’, ‘]’.
Empty string “” → valid.
Can there be other characters? → No.
Is “)(“ valid? → No, order matters.
Expected time/space complexity? → O(n) time, O(n) space is typical.

3. Work through examples

Input	Output	Reason
`"()"`	`true`	Simple pair
`"()[]{}"`	`true`	Multiple valid pairs
`"(]"`	`false`	Mismatched types
`"([)]"`	`false`	Wrong order
`"{[]}"`	`true`	Nested valid

November 9, 2025