update project structure

leetcode_py/20.py

@@ -0,0 +1,49 @@
+# give a string s containing just '(', ')' and else
+# determine if the input is valid
+
+
+class Solution:
+    def isValid(self, s: str) -> bool:
+        """
+        # too slow
+        symbol_dict = {"(": ")", "{": "}", "[": "]"}
+        stack = []
+        for i in s:
+            try:
+                stack_top = stack.pop()
+            except IndexError:
+                stack.append(i)
+                continue
+
+            try:
+                if symbol_dict[stack_top] == i:
+                    continue
+
+                 stack.append(stack_top)
+
+            except KeyError:
+                return False
+
+            stack.append(i)
+
+        if stack:
+            return False
+
+        return True
+        """
+
+        # Optimized solution
+        bracket_map = {")": "(", "}": "{", "]": "["}
+        stack = []
+
+        for char in s:
+            if char in bracket_map:
+                top_element = stack.pop() if stack else "#"
+
+                if bracket_map[char] != top_element:
+                    return False
+
+            else:
+                stack.append(char)
+
+        return not stack