I found it on another forum and after checking it, was impressed with its clever design.
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+-------+-------+-------+
| . 2 . | . . . | . 7 . |
| 9 . . | 5 . 8 | . . 4 |
| . . . | . . . | . . . |
+-------+-------+-------+
| 4 . . | . 3 . | . . 8 |
| . 7 . | . 9 . | . 2 . |
| 6 . . | . 1 . | . . 5 |
+-------+-------+-------+
| . . . | . . . | . . . |
| 5 . . | 6 . 4 | . . 1 |
| . 3 . | . . . | . 9 . |
+-------+-------+-------+