Update solution 020 [Python3]

Author: chakyam

solution/020.Valid Parentheses/Solution.py

@@ -21,4 +21,26 @@ def isValid(self, s):
                 pass
             else:
                 f=False
-                return f
+                return f
+
+class Solution():
+    def isValid(self,s):
+        """
+        :type s: str
+        :rtype: bool
+        """
+        left=['(','{','[']
+        right={ ')':'(',
+                ']':'[',
+                '}':'{' }
+        stack=[]
+        for i in s:
+            if i in left:
+                stack.append(i)
+            elif stack and right[i] == stack.pop():
+                continue
+            else:
+                return False
+        if stack:
+            return False
+        return True