feat(content): function signatures + test cases

backend/data/questions/add-two-numbers-ii.yaml

@@ -10,6 +10,28 @@ categories:
 patterns:
   - linkedlist-reversal
 
+function_signature: "def add_two_numbers(l1: ListNode, l2: ListNode) -> ListNode:"
+
+test_cases:
+  visible:
+    - input: { l1: [7, 2, 4, 3], l2: [5, 6, 4] }
+      expected: [7, 8, 0, 7]
+    - input: { l1: [2, 4, 3], l2: [5, 6, 4] }
+      expected: [8, 0, 7]
+    - input: { l1: [0], l2: [0] }
+      expected: [0]
+  hidden:
+    - input: { l1: [9, 9, 9], l2: [1] }
+      expected: [1, 0, 0, 0]
+    - input: { l1: [5], l2: [5] }
+      expected: [1, 0]
+    - input: { l1: [1, 2, 3, 4, 5], l2: [6, 7, 8, 9] }
+      expected: [1, 9, 1, 3, 4]
+    - input: { l1: [9, 9, 9, 9, 9], l2: [9, 9, 9, 9, 9] }
+      expected: [1, 9, 9, 9, 9, 8]
+    - input: { l1: [1], l2: [9, 9, 9, 9] }
+      expected: [1, 0, 0, 0, 0]
+
 description: |
   You are given two **non-empty** linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.