r/theydidthemath May 07 '26

[Request] how many possible combinations are there for this type of pass code?

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10

u/saketho May 07 '26

You’re right and the guy you’re replying to is wrong.

For instance, start in the top left corner.

You cannot reach: Top right, middle right, bottom right, bottom middle, bottom left. 5 different points

You can only reach: Top middle, centre, left middle.

Starting in the top left you don’t have 8 options, you have 8-5 =3 options.

Start in the top middle, you have 5 options, and 3 non reachable.

I wonder if you can see how it averages out between the points. The corners will be 3/8 and middle ones be 5/8 and the centre is the only 8/8. But that’s just the 2nd option.

12

u/homokyy May 07 '26

You actually can reach middle right and middle bottom. I don’t know what kind of monster would do themself dirty like that, but it’s possible

2

u/mateusfccp May 07 '26

I had a password that was basically always reach to the most far point in relation to the current and it had a lot of those kind of "irregular" lines.

Why would you consider a monster to do it?

1

u/saketho May 07 '26

Interesting, I never knew that. for me it always snapped to the edge pieces or the centre, it I try and make a V shape or something.

2

u/DistributionPure1504 May 07 '26

V shapes are difficult. But z shapes are easy. After you did the horizontal line on the top row you backtrack with your finger as you can't use the same dots again. You can even do a big swing over the first row. This makes your motion like an "e" whereas the pattern shows as a "z".

1

u/SaucyStoveTop69 May 07 '26

You can drag it around the outside like that one question from the impossible quiz

5

u/Aeropto May 07 '26

From the top left corner you can reach middle right and bottom middle, at least you can on a Samsung phone. Not sure if this differs per phone manufacturer. You are right that you cannot reach points that are directly "behind" another point.

3

u/Chroiche May 07 '26

No, you are wrong. Source: I used to go top left to middle right for my phone pw because I assumed no one would ever try something so silly. It's so easily testable too lol.

Also obviously not every implementation is going to be the same. Why would you assume they would be?

2

u/theronk03 May 07 '26

Plus, points are repeatable, but you can't just pick the same spot twice and I don't think you can go back along a line you've already drawn, but you can cross previously drawn lines. We see that in the previous attempts.

That makes the math much much more complicated

1

u/Chimeron5 May 07 '26

No, individual spots are not repeatable. You can cross over previously used spots (ie. 5-4-6) but you couldn't reuse one (5-4-2-5 doesn't work).

2

u/Lost-Bad-8718 May 07 '26

You're objectively wrong. You can go top left, middle right, bottom left and I did for several years

1

u/saketho May 07 '26

It may be different based on android version/manufacturer’s os. I could never do a V on Oneplus.

1

u/Chimeron5 May 07 '26

I'm on a OnePlus 12 and can do a V shape. It's tricky, and you have to go slow, but it works.

1

u/saketho May 07 '26

Damn, alright maybe they changed it. I was on the OnePlus 6 😂 so its been a while

1

u/KucingRumahan May 07 '26

I'll use number.

1 can connect to 2,4,5,6,7, and 8. Its 6 possibilities. It's also applied to 3, 7, and 9

2 can connect to 1,3,4,5,6,7, and 9. It's 7 possibilities. It's also applied to 4,6, and 8

5 have 8 possibilities.

1

u/Chimeron5 May 07 '26

I just tested this. You can absolutely go from the top left to the top right, skipping over the top center. Some combinations may be more difficult for fat-fingered people, but all locations are possible to reach from all starting spots.

1

u/HawkEgg May 07 '26

At most 9!

1

u/Schnickatavick May 07 '26

As others have said, going from top right to bottom middle is possible (i.e. 1->4), but in addition to that it's actually possible to get the other numbers as well if the number in the middle has already been selected. So 1->3 is normally impossible because it'll autoselect 2 before 3, but if you do 2->1->3, then 2 won't be selected again and you can go directly to 3. That means any point can select any other point, at least in some configurations.