feat(content): function signatures + test cases

backend/data/questions/binary-tree-tilt.yaml

@@ -10,6 +10,32 @@ patterns:
   - dfs
   - tree-traversal
 
+function_signature: "def find_tilt(root: TreeNode) -> int:"
+
+test_cases:
+  visible:
+    - input: { root: [1, 2, 3] }
+      expected: 1
+    - input: { root: [4, 2, 9, 3, 5, null, 7] }
+      expected: 15
+    - input: { root: [21, 7, 14, 1, 1, 2, 2, 3, 3] }
+      expected: 9
+  hidden:
+    - input: { root: [] }
+      expected: 0
+    - input: { root: [1] }
+      expected: 0
+    - input: { root: [1, 2, null] }
+      expected: 2
+    - input: { root: [1, null, 3] }
+      expected: 3
+    - input: { root: [0, 0, 0] }
+      expected: 0
+    - input: { root: [5, 5, 5, 5, 5, 5, 5] }
+      expected: 0
+    - input: { root: [1, 2, 3, 4, null, 5, 6] }
+      expected: 11
+
 description: |
   Given the `root` of a binary tree, return *the sum of every tree node's **tilt***.