feat(content): function signatures + test cases

backend/data/questions/adding-spaces-to-a-string.yaml

@@ -10,6 +10,26 @@ categories:
 patterns:
   - two-pointers
 
+function_signature: "def add_spaces(s: str, spaces: list[int]) -> str:"
+
+test_cases:
+  visible:
+    - input: { s: "LeetcodeHelpsMeLearn", spaces: [8, 13, 15] }
+      expected: "Leetcode Helps Me Learn"
+    - input: { s: "icodeinpython", spaces: [1, 5, 7, 9] }
+      expected: "i code in py thon"
+    - input: { s: "spacing", spaces: [0, 1, 2, 3, 4, 5, 6] }
+      expected: " s p a c i n g"
+  hidden:
+    - input: { s: "abc", spaces: [1] }
+      expected: "a bc"
+    - input: { s: "abc", spaces: [0] }
+      expected: " abc"
+    - input: { s: "EnjoyYourCoffee", spaces: [5, 9] }
+      expected: "Enjoy Your Coffee"
+    - input: { s: "hello", spaces: [1, 2, 3, 4] }
+      expected: "h e l l o"
+
 description: |
   You are given a **0-indexed** string `s` and a **0-indexed** integer array `spaces` that describes the indices in the original string where spaces will be added. Each space should be inserted **before** the character at the given index.