feat: finish valid parentheses in python

Author: bujosa

alternative/easy/valid_parentheses.py

@@ -0,0 +1,19 @@
+def is_valid(s):
+    stack = []
+    for c in s:
+        if c in "([{":
+            stack.append(c)
+        elif c == ')' and (not stack or stack.pop() != '('):
+            return False
+        elif c == ']' and (not stack or stack.pop() != '['):
+            return False
+        elif c == '}' and (not stack or stack.pop() != '{'):
+            return False
+    return not stack
+
+# Test cases
+assert is_valid("()") == True
+assert is_valid("()[]{}") == True
+assert is_valid("(]") == False
+assert is_valid("([)]") == False
+assert is_valid("{[]}") == True