Create longest_valid_paranthesis.py

made necessary changes!

Author: AryanMankame

strings/longest_valid_paranthesis.py

@@ -0,0 +1,32 @@
+def longest_valid_paranthesis(self, s: str) -> int:
+        """
+       Returns the length of the longest valid paranthesis
+        >>> longest_valid_paranthesis('(()')
+        2
+        >>> longest_valid_paranthesis(')()())')
+        4
+        >>> longest_valid_paranthesis('')
+        0
+        >>> longest_valid_paranthesis(''(())))((()(()()()())
+        8
+        """
+        stack = []
+        preceeding_matched = 0
+        res = 0
+        for char in s:
+            if char == "(":
+                stack.append(preceeding_matched)
+                preceeding_matched = 0
+            else:
+                if stack:
+                    preceeding_matched += 1 + stack.pop()
+                else:
+                    res = max(res, preceeding_matched)
+                    preceeding_matched = 0
+        
+        res = max(res, preceeding_matched)
+        
+        while stack:
+            res = max(res, stack.pop())
+        
+        return res * 2