Observations on wriggle puzzles (added 2010)

The wriggle-rule relaxes the classic Rush-Hour rule just a little, by allowing the blocks to bend (and thus wriggle). You still cannot drag an object side-ways, only backwards or forwards, from one end or the other. It turns out this modest modification to the rule has a big impact on the puzzle behaviour. Most notably very long wriggles are possible and many more states are reachable, which in turn means even more complexity and variety can be packed into a small area.

For almost 8 years there was no methodical search of the wriggle-rule puzzle space so exactly was was achievable on the smaller grid (such as 5x5) was an unknown. During 2010 Bob Henderson (USA) decided it was time to find out and discovered that there was a huge wealth of untapped complexity, even on the 4x4 grid [Read more].

Development notes (added 2022)

Somewhat surprisingly, my humble Wriggle app gets the accolade for being the first ever snake puzzle game. I keep waiting for something to sneak into the ultra-handy quick reference table ahead of Wriggle, but so far nothing has challenged it for top slot.

Joel once asked me to write some background notes describing the inspiration behind Wriggle and I never quite got around to that, although I have often pondered exactly what I would say. The wording above suggests Wriggle might be inspired by Rush-Hour, but I know this not to be true. The parallel with Rush-Hour was an afterthought and simply a good way of describing how the mechanic worked in relation to something already familiar.

So, where did the inspiration come from? Let's try and rewind the clock...

Way back in 2003 I was pretty much at my peak, developing my puzzling ideas into applets. I had a solid core framework of classes which I was rapidly adding new interfaces to, in order to support new UI interactions. Mouse click and drag were probably added on a wet Sunday afternoon, simply because they were next on the list (and I'd finally understood that chapter of the book!). I can clearly remember I did not have a puzzle concept in mind, but was hopeful that as soon as I could paint something on the screen and drag it around then inspiration would strike. Looking back now, after nearly 20 years, I think this pretty much summarises what happened next...

Yay, it compiles and runs... and voila one circle is now a wobbly line of circles. Ok... that's too many circles, let's retain just the last few. Haha, that wriggles like a worm. Cute. Let's paint that one red and add a blue one (oops... I need a mouse-up handler also. Done). Yup - two worms. OK let's snap that to a grid and add collision detection. Done. OK so can I now swap red and blue by wriggling them. Nah... well maybe... oh yes! Hmmm... that was non-trivial, but why? And can I make it even harder? Oh!!!!

And thus a puzzle (and puzzle genre) was born. [Discover more]