feature: valid parentheses revisit

stack/ValidParentheses.py

@@ -1,13 +1,12 @@
 # O(n) time || O(n) space
 def is_valid(self, s: str) -> bool:
-    close_to_open, stack = {")": "(", "]": "[", "}": "{"}, []
-    for c in s:
-        if c not in close_to_open:
-            stack.append(c)
-        elif stack:
-            if stack.pop() != close_to_open[c]:
+    brackets = {')': '(', ']': '[', '}': '{'}
+    stack = []
+    for br in s:
+        if br in brackets:
+            if not stack or stack.pop() != brackets[br]:
                 return False
         else:
-            return False
+            stack.append(br)
 
     return not stack

stack/test/test_is_valid.py

@@ -13,6 +13,12 @@ def test_is_valid_1(self):
     def test_is_valid_2(self):
         self.assertEqual(False, is_valid(self, "(]"))
 
+    def test_is_valid_3(self):
+        self.assertEqual(True, is_valid(self, "{[]}"))
+
+    def test_is_valid_4(self):
+        self.assertEqual(False, is_valid(self, "]"))
+
 
 if __name__ == '__main__':
     unittest.main()