Dsa
Monotonic Stack
Hard
Largest Valid Parentheses
Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring. You need to implement the function `longest_valid_parentheses(s: str) -> int`.
### Input
A single line containing a string of parentheses.
### Output
An integer representing the length of the longest valid parentheses substring.
### Example
Input:
)()())
Output:
4
Key concepts
monotonic_stackparenthesesstring
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