feat(content): function signatures + test cases

backend/data/questions/longest-happy-string.yaml

@@ -10,6 +10,35 @@ patterns:
   - greedy
   - heap
 
+function_signature: "def longest_happy_string(a: int, b: int, c: int) -> str:"
+
+test_cases:
+  visible:
+    - input: { a: 1, b: 1, c: 7 }
+      expected: "ccaccbcc"
+      note: "Other valid outputs like 'ccbccacc' are also accepted"
+    - input: { a: 7, b: 1, c: 0 }
+      expected: "aabaa"
+  hidden:
+    - input: { a: 0, b: 0, c: 1 }
+      expected: "c"
+    - input: { a: 1, b: 1, c: 1 }
+      expected: "abc"
+      note: "Any permutation is valid"
+    - input: { a: 2, b: 2, c: 1 }
+      expected: "aabbc"
+      note: "Multiple valid outputs"
+    - input: { a: 0, b: 8, c: 11 }
+      expected: "ccbccbbccbbccbbccbc"
+      note: "Length should be 19"
+    - input: { a: 3, b: 0, c: 0 }
+      expected: "aa"
+    - input: { a: 0, b: 0, c: 2 }
+      expected: "cc"
+    - input: { a: 4, b: 4, c: 4 }
+      expected: "aabbccaabbcc"
+      note: "Multiple valid outputs"
+
 description: |
   A string `s` is called **happy** if it satisfies the following conditions: