feat(content): function signatures + test cases

backend/data/questions/binary-tree-level-order-traversal-ii.yaml

@@ -10,6 +10,26 @@ patterns:
   - bfs
   - tree-traversal
 
+function_signature: "def level_order_bottom(root: TreeNode) -> list[list[int]]:"
+
+test_cases:
+  visible:
+    - input: { root: [3, 9, 20, null, null, 15, 7] }
+      expected: [[15, 7], [9, 20], [3]]
+    - input: { root: [1] }
+      expected: [[1]]
+    - input: { root: [] }
+      expected: []
+  hidden:
+    - input: { root: [1, 2, 3, 4, 5, 6, 7] }
+      expected: [[4, 5, 6, 7], [2, 3], [1]]
+    - input: { root: [1, 2, null, 3, null, 4] }
+      expected: [[4], [3], [2], [1]]
+    - input: { root: [1, null, 2, null, 3] }
+      expected: [[3], [2], [1]]
+    - input: { root: [-10, 9, 20, null, null, 15, 7] }
+      expected: [[15, 7], [9, 20], [-10]]
+
 description: |
   Given the `root` of a binary tree, return *the bottom-up level order traversal of its nodes' values* (i.e., from left to right, level by level from leaf to root).