Ultramarathon
(Published on 24. November 2025, 17:37 by oklux)
Rules:
- Normal Sudoku rules apply.
- Ultramarathon (see example): Draw a single continuous, non-branching line that moves from cell to cell orthogonally. Separate segments of the line may be orthogonally adjacent (share a cell edge), but the line may not revisit a cell or cross itself. The line must start and end at the outer corners of the grid (e.g., r1c1 and r1c9). There are 9 Checkpoint Cells, one in each row, column, and 3×3 box, containing the digits 1–9 once each. The line goes through every Checkpoint Cell exactly once, and must start and end in one. The line cannot re-enter a 3×3 box it has already been in. The value of a Checkpoint Cell is double its digit. Two connected Checkpoints' values sum to the digits on the line between them. Each Checkpoint's digit indicates how many cells the line passes through in its own box. The line cannot cross a border marked with a barrier.
- A balloon's digit indicates the number of line cells in the 3×3 area around them, including themselves.
Solution code: Row 8, left to right (9 digits)
Comments
yesterday, 01:18 by Angel
Great puzzle and some great ideas throughout.
on 25. November 2025, 14:12 by flutchman
The rules seem a bit daunting, but definitely worth the effort!
Cool puzzle.
on 25. November 2025, 13:18 by lmdemasi
Really cool construction, and the solve has some interesting ideas and logic to it.
on 25. November 2025, 10:54 by oklux
Added example and clarified rules.
on 25. November 2025, 07:11 by Marshal on Mars
Is the 1-cell-wide, non-branching nature of the line meant to convey that two cells that are both on the line and are adjacent in the grid must be directly connected on the line? (i.e. the line cannot touch itself orthogonally) Or is that not necessarily conveyed and to be deduced?
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No, it is not meant to convey that . The line can touch itself, but it never crosses itself. I might clarify the rules once again, and possibly even add an example. Sorry for the confusion.
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Thanks! I was thinking I had broken the puzzle right out of the gate. ^_^; I'll soldier on with the clarification.
on 25. November 2025, 03:44 by oklux
Clarified rules
on 24. November 2025, 23:55 by lmdemasi
If a balloon is a checkpoint, does the digit or the value count the number of line cells in the 3x3 area?
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Oh good question, it's the digit that counts it. I'll add that to the rules.
