add leetcode 20

leetcode/20.py

@@ -0,0 +1,26 @@
+# give a string s containing just '(', ')' and else
+# determine if the input is valid
+
+
+class Solution:
+    def isValid(self, s: str) -> bool:
+        symbol_dict = {"(": ")", "{": "}", "[": "]"}
+        stack = []
+        for i in s:
+            try:
+                stack_top = stack.pop()
+            except IndexError:
+                continue
+
+            try:
+                if symbol_dict[stack_top] == i:
+                    continue
+            except KeyError:
+                return False
+
+            stack.append(i)
+
+        if stack:
+            return False
+
+        return True