Project Euler Forum

I would like to start by expressing my sincere appreciation for the work that all of you do to maintain Project Euler. I have greatly enjoyed solving some of these problems over the last decade.

This is my first post, and it is quite likely that I am missing something simple here. The problem states that there are 389,488 passwords that are valid on a 3 x 3 grid. I don't understand this; isn't the upper bound for the number of passwords 9! = 362,880?

Thank you for your help.

I imagine that would be true if all passwords were 9 digits in length.

You're right; that's exactly what I was missing. Thank you for the quick reply.

Problem 879 (View Problem)

(adding problem link missing from first post)

Is it possible to enter e.g 1-to-6 or 1-to-8 - passing over no intermediate spots - in this interface? Or is it limited to horizontal, vertical and 45-degree diagonal strokes?

(I've seen people using this style of "password" to unlock their phones but I've never tried it myself.)

I imagine reproducing the given 3x3 result will clarify this for me, of course!

timday wrote: Tue Jul 09, 2024 2:43 pm Is it possible to enter e.g 1-to-6 or 1-to-8 - passing over no intermediate spots - in this interface? Or is it limited to horizontal, vertical and 45-degree diagonal strokes?

Yes, straight line segments are permitted in any direction.