8
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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.

enter image description here

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

enter image description here

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.
As with the Knights problem, I added additional rules.

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

enter image description here

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.

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  • $\begingroup$ I still don't understand how you got to the solution. Can you at least tell how you got even one of the numbers? $\endgroup$ – Sid May 9 at 15:04
  • $\begingroup$ @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. $\endgroup$ – Weather Vane May 9 at 15:07
  • $\begingroup$ And, I wrote the code myself. The solution wasn't found by an online solver. $\endgroup$ – Weather Vane May 9 at 15:17
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    $\begingroup$ 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. $\endgroup$ – Sid May 9 at 15:22

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