Add problem 678 - Valid Parenthesis String

Author: anirudhology

problems/greedy/valid_parenthesis_string.py

@@ -0,0 +1,37 @@
+class ValidParenthesisString:
+    @staticmethod
+    def checkValidString(s: str) -> bool:
+        # Special case
+        if s is None or not len(s):
+            return True
+        # Count of minimum and maximum open parentheses
+        min_open, max_open = 0, 0
+        # Traverse through the string
+        for c in s:
+            # If it is a left parenthesis, it means you have one
+            # more open parenthesis to worry about
+            if c == '(':
+                min_open += 1
+                max_open += 1
+            # If it is right parenthesis, it means you have one
+            # less open parenthesis to worry about
+            elif c == ')':
+                min_open -= 1
+                max_open -= 1
+            # If it is *, it means there are three cases
+            # 1. If we make it as ), then we have one less open parenthesis to worry about
+            # 2. If we make it as (, then we have one more open parentheses
+            # to worry about
+            # 3. No impact at all
+            elif c == '*':
+                min_open -= 1
+                max_open += 1
+
+            # There are more closing parentheses, then opening ones
+            if max_open < 0:
+                return False
+            # We can't have negative open parenthesis count
+            if min_open < 0:
+                min_open = 0
+
+        return min_open == 0

tests/greedy/valid_parenthesis_string_test.py

@@ -0,0 +1,42 @@
+import unittest
+
+from problems.greedy.valid_parenthesis_string import ValidParenthesisString
+
+
+class TestValidParenthesisString(unittest.TestCase):
+
+    def setUp(self):
+        self.valid_parenthesis_string = ValidParenthesisString()
+
+    def test_check_valid_string(self):
+        # Test null input
+        self.assertTrue(self.valid_parenthesis_string.checkValidString(None))
+
+        # Test empty string
+        self.assertTrue(self.valid_parenthesis_string.checkValidString(""))
+
+        # Test valid strings
+        self.assertTrue(self.valid_parenthesis_string.checkValidString("()"))
+        self.assertTrue(self.valid_parenthesis_string.checkValidString("(*)"))
+        self.assertTrue(self.valid_parenthesis_string.checkValidString("(*))"))
+
+        # Test invalid strings
+        self.assertFalse(self.valid_parenthesis_string.checkValidString(")"))
+        self.assertFalse(self.valid_parenthesis_string.checkValidString(")("))
+        self.assertTrue(self.valid_parenthesis_string.checkValidString("((*)"))
+        self.assertFalse(self.valid_parenthesis_string.checkValidString("((*))("))
+
+    def test_edge_cases(self):
+        # Test string with only one *
+        self.assertTrue(self.valid_parenthesis_string.checkValidString("*"))
+
+        # Test string with multiple *
+        self.assertTrue(self.valid_parenthesis_string.checkValidString("***"))
+
+        # Test strings with nested parentheses
+        self.assertTrue(self.valid_parenthesis_string.checkValidString("(())"))
+        self.assertFalse(self.valid_parenthesis_string.checkValidString("(()))"))
+
+
+if __name__ == '__main__':
+    unittest.main()