Syntax error Program to find length of longest valid parenthesis from given string in Python

Program to find length of longest valid parenthesis from given string in Python

Suppose we have a string s. This s consists of opening and closing parenthesis only. We have to find the length of the longest valid (well-formed) parentheses substring. So if the input is like “))(())())”, then the result will be 6, as the valid string is “(())()”.

To solve this, we will follow these steps −

  • Make a stack, and insert -1., set ans := 0

  • for i in range 0 to length of stack – 1

    • if s[i] is opening parentheses, then insert i into stack

    • otherwise

      • if stack is not empty and top of stack is not -1 and s[stack top] is opening parentheses, then

        • top element from stack

        • ans := max of ans and i – stack top

      • otherwise insert i into stack

  • return ans

Example 

Let us see the following implementation to get a better understanding −

 Live Demo

class Solution(object):
   def solve(self, s):
      stack = [-1]
      ans = 0
      for i in range(len(s)):
         if s[i] == "(":
            stack.append(i)
         else:
            if stack and stack[-1]!=-1 and s[stack[-1]] == "(":
               stack.pop()
               ans = max(ans,i - stack[-1])
            else:
               stack.append(i)
      return ans
ob = Solution()
print(ob.solve("))(())())"))

Input

"))(())())"

Output

6
Updated on: 2020-12-22T06:27:58+05:30

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