feat(content): hidden test cases

backend/data/questions/find-the-duplicate-number.yaml

@@ -27,6 +27,12 @@ test_cases:
       expected: 2
     - input: { nums: [1, 4, 4, 2, 4] }
       expected: 4
+    - input: { nums: [1, 2, 3, 4, 5, 6, 7, 8, 9, 5] }
+      expected: 5
+    - input: { nums: [2, 5, 9, 6, 9, 3, 8, 9, 7, 1] }
+      expected: 9
+    - input: { nums: [1, 1, 2] }
+      expected: 1
 
 description: |
   Given an array of integers `nums` containing `n + 1` integers where each integer is in the range `[1, n]` inclusive.