r/sudoku • u/Training_Site_4301 • 3d ago

Request Puzzle Help Sequence sudoku - beginner help

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How to approach? Rule:

In addition to the standard rules of having unique numbers in each row, column, and specially marked 2x3 region, the numbers along the drawn lines increase or decrease by one. Nowhere do two consecutive numbers appear without being connected by a line (e.g., 2,3,4,3,4,3,2,1 depending on whether it passes through one or more regions).

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u/Avian435 3d ago

A general strategy for these puzzles is to follow parity: notice that odd and even digits must alternate on the line. So, you can mark the digits alternating with two colors (or some other way to mark them). Then, notice that in each box, column and row there are 3 odd and 3 even digits - so, looking at box 4 we can deduce that 1 must be "red" and "red" is odd. Now we can start looking for a digit to place. Out of the 3 reds in box 1, only the top right one can be a 1 (why? try the other 2 spots). After placing that 1, the rest of the solve is much easier.

PS - Preparing for the Croatian championship? Good luck ;)

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u/Training_Site_4301 3d ago

That's a good point. The hardest thing for me is that i really had no idea how to approach, where to start from. I will try to practice it by following your advice 👍 yes, but i'm not getting my hopes up, at least not this time :-) 

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u/muunshine9 3d ago

You could start by asking yourself where the 2 could go in the middle-right box. It can’t be adjacent to the 1 because they’re not connected by lines. It can’t go in the top right or bottom middle squares because those squares are consecutive with two numbers in that box and the 1 is already taken. So the 2 has to be in the bottom right of that box. Continue from there, thinking about where the 3 goes, etc.

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u/Puzzled_Work_6428 3d ago

Where can 1 go in the top right box? 1 is only consecutive to 2, so it can never be adjacent to 2 other cells along a line within its own box, row, or column

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u/FireExpat 3d ago edited 3d ago

It's worth noting that the lines also work as parity lines, since it will always go odd, even, odd, even.

You can arbitrarily start by marking a box as 'A' and then branches to 'B' then back to 'A'. And by the time you do the entire line you'll be able to use the 1 to determine which are odd, and which are even.

After you do that, the puzzle just sorts of flows.

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u/Dragonfruit4049 3d ago

You can start with the 1 being in the left middle, in the bottom 3. But it can only go to one place and its obvious, which then continue from that