Puzzle of the day - Sudoku Rossini

The arrows outside the grid indicate that the nearest three digits in the corresponding direction are in ascending or descending order (the highest number is always in the direction of the arrow). All possible arrows are given, so if there is no arrow, the first three digits do not form an increasing sequence in either direction.

• Why the [computer-puzzle] tag? Commented May 8, 2020 at 21:39
• ^ Does that mean it's just too hard to solve by hand? (Because if so, I've just wasted a lot of minutes trying!) Commented May 9, 2020 at 9:09
• At first I thought it meant a consecutive sequence but that is impossible. Commented May 9, 2020 at 9:20
• Can you give maybe 1/2 more cells as a hint please?
– user68905
Commented May 9, 2020 at 11:25
• @WeatherVane same, I can only get 2/3 confirmed numbers
– user68905
Commented May 9, 2020 at 12:36

Here is my solution:

None of the inward lines-of-three around the edges have an increasing or
decreasing sequence except where marked by arrows showing their direction.

The question tags allow a computer solution, so I built on my answer to
Knights in a Complete Sudoku Board which used C code to solve it.

I set out to solve it by hand, on the basis of runs-of-three being consecutive.

If so, in diagram B some of the runs can be filled immediately.
In diagram C the only possible sequence for the second arrow across is $$6 \ 7 \ 8$$.
But it is obvious there is nowhere to place a $$3$$ in that corner box.

So in view of a comment under the question and no hand-made solution posted within
several hours I worked out this answer. Some may say it's not very logical and I
only have to dial it into a program but that simply isn't true. It's just a different
logical process, and it took me longer than it usually does to solve a Sudoku by hand.

I did not find any other solution.

• I still don't understand how you got to the solution. Can you at least tell how you got even one of the numbers?
– Sid
Commented May 9, 2020 at 15:04
• @Sid is that required? It's a C program which finds a solution without a brute force search. That is allowed by the computer-puzzle tag. It says it is for questions that are dependent on that means. Commented May 9, 2020 at 15:07
• And, I wrote the code myself. The solution wasn't found by an online solver. Commented May 9, 2020 at 15:17
• Oh, you wrote a program for it? That's okay. I didn't understand how you reached to your answer. That's kinda what I was asking for it.
– Sid
Commented May 9, 2020 at 15:22