feat(content): function signatures + test cases

backend/data/questions/longest-valid-parentheses.yaml

@@ -11,6 +11,32 @@ patterns:
   - dynamic-programming
   - monotonic-stack
 
+function_signature: "def longest_valid_parentheses(s: str) -> int:"
+
+test_cases:
+  visible:
+    - input: { s: "(()" }
+      expected: 2
+    - input: { s: ")()())" }
+      expected: 4
+    - input: { s: "" }
+      expected: 0
+  hidden:
+    - input: { s: "()" }
+      expected: 2
+    - input: { s: "()()" }
+      expected: 4
+    - input: { s: "((()))" }
+      expected: 6
+    - input: { s: "(()()" }
+      expected: 4
+    - input: { s: ")()()((" }
+      expected: 4
+    - input: { s: "((((((" }
+      expected: 0
+    - input: { s: "))))))" }
+      expected: 0
+
 description: |
   Given a string containing just the characters `'('` and `')'`, return *the length of the longest valid (well-formed) parentheses substring*.