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Longest Valid Parentheses

Certification: Advanced Level Accuracy: 0% Submissions: 0 Points: 15

Write a C program to find the length of the longest valid (well-formed) parentheses substring. Given a string containing just the characters '(' and ')', find the length of the longest valid parentheses substring.

Example 1
    
  
  • Input: s = "(()"
    • 
  
  • Output: 2
    • 
  
  • Explanation: 
    
      
      
    • Step 1: The longest valid parentheses substring is "()".
      • 
      
    • Step 2: This substring has length 2.
      • 
      
    • Step 3: Therefore, the answer is 2.
      • 
    
    
  
    •
Example 2
    
  
  • Input: s = ")()())"
    • 
  
  • Output: 4
    • 
  
  • Explanation: 
    
      
      
    • Step 1: The longest valid parentheses substring is "()()".
      • 
      
    • Step 2: This substring has length 4.
      • 
      
    • Step 3: Therefore, the answer is 4.
      • 
    
    
  
    •
Constraints
    
  
  • 0 ≤ strlen(s) ≤ 3 * 10^4
    • 
  
  • s[i] is '(' or ')'
    • 
  
  • Time Complexity: O(n)
    • 
  
  • Space Complexity: O(n)
    •
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Hint
Solution

Solution Hints

    
  
  • Use a stack to keep track of indices of characters.
    • 
  
  • Push -1 initially to handle base case.
    • 
  
  • For each '(', push its index onto the stack.
    • 
  
  • For each ')', pop from stack and calculate current valid length.
    • 
  
  • Keep track of the maximum length found so far.
    • 
  
  • If stack becomes empty after popping, push current index.
    •

Steps to solve by this approach:

 Step 1: Initialize a stack and push -1 as the base for calculating lengths.
 Step 2: Iterate through each character in the string.
 Step 3: If the character is '(', push its index onto the stack.
 Step 4: If the character is ')', pop from the stack.
 Step 5: If stack becomes empty after popping, push the current index as new base.
 Step 6: Otherwise, calculate the current valid length using current index minus top of stack.
 Step 7: Keep track of the maximum length encountered and return it.

Submitted Code :