Longest Valid Parentheses

Problem

Given a string containing only '(' and ')', return the length of the longest valid (well-formed) parentheses substring.

Approach

• Use a stack to store indices.
• Initialize the stack with -1.
• Push indices of '('.
• For ')', pop from the stack.
• If the stack becomes empty, push the current index.
• Otherwise, update the maximum valid length.

Time Complexity

O(n)

Space Complexity

O(n)

Language

Java