feat(content): hidden test cases

backend/data/questions/brace-expansion-ii.yaml

@@ -11,6 +11,28 @@ patterns:
   - backtracking
   - dfs
 
+function_signature: "def brace_expansion_ii(expression: str) -> list[str]:"
+
+test_cases:
+  visible:
+    - input: { expression: "{a,b}{c,{d,e}}" }
+      expected: ["ac", "ad", "ae", "bc", "bd", "be"]
+    - input: { expression: "{{a,z},a{b,c},{ab,z}}" }
+      expected: ["a", "ab", "ac", "z"]
+  hidden:
+    - input: { expression: "a" }
+      expected: ["a"]
+    - input: { expression: "{a,b}" }
+      expected: ["a", "b"]
+    - input: { expression: "{a,b}c" }
+      expected: ["ac", "bc"]
+    - input: { expression: "a{b,c}d" }
+      expected: ["abd", "acd"]
+    - input: { expression: "{a}{b}" }
+      expected: ["ab"]
+    - input: { expression: "{{a}}" }
+      expected: ["a"]
+
 description: |
   Under the grammar given below, strings can represent a set of lowercase words. Let `R(expr)` denote the set of words the expression represents.