Added solution

Author: avidLearnerInProgress

longest_valid_parentheses.py

@@ -0,0 +1,29 @@
+class Solution:
+    def longestValidParentheses(self, s: str) -> int:
+        if not s: return 0
+        result, ind = 0, -1
+        count, len_ = 0, 0
+        for i in range(len(s)):
+            len_ += 1
+            if s[i] == '(':
+                count += 1
+            if s[i] == ')':
+                count -= 1
+            if count == 0 and len_ > result:
+                result = len_
+            if count < 0:
+                len_, count = 0, 0
+            
+        len_, count = 0, 0
+        for i in range(len(s)-1, -1, -1):
+            len_ += 1
+            if s[i] == ')':
+                count += 1
+            if s[i] == '(':
+                count -= 1
+            if count == 0 and len_ > result:
+                result = len_
+            if count < 0:
+                len_, count = 0, 0
+        
+        return result