I'm unable to process images directly. Could you please describe the problem statement in text form?

For reference, if your problem is the Longest Valid Parentheses (finding the length of the longest well-formed substring of parentheses), here's a common solution using a stack:

Solution for Longest Valid Parentheses

Approach: Use a stack to track indices of parentheses. Push -1 as a base marker for valid substring start.

Steps:

1. Initialize a stack with -1 (base index).
2. Iterate over each character in the string:
   • If the character is '(', push its index to the stack.
   • If the character is ')', pop the top element:
     • If the stack becomes empty, push the current index as the new base.
     • Else, calculate the length of the valid substring as current index - stack.top() and update the maximum length.

Code:

def longestValidParentheses(s: str) -> int:
    stack = [-1]
    max_len = 0
    for i in range(len(s)):
        if s[i] == '(':
            stack.append(i)
        else:
            stack.pop()
            if not stack:
                stack.append(i)
            else:
                max_len = max(max_len, i - stack[-1])
    return max_len

This solution runs in O(n) time and space, where n is the length of the string.

Please share the exact problem text if this isn't what you're looking for!

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