How To Solve "Cave" Logic Puzzles

We take a look at a staple from the US Puzzle Championships over the year's, the "Cave" puzzle. This puzzle can be found at the following site (but you'll need to register to unlock the files):
wpc.puzzles.com...
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▶SOFTWARE◀
We mainly use Duncan's Sudoku Solver, which is available at www.littlegogs....
▶ABOUT US◀
Hi! We're Simon Anthony and Mark Goodliffe, two of the UK's most enthusiastic puzzle solvers. We have both represented the UK at the World Sudoku Championships and the World Puzzle Championships. We're also "cryptic crossword" aficionados. Mark is the eleven-time winner of The Times championship and Simon is the former record holder for most consecutive correct solutions to The Listener crossword. We hope we can help your puzzle solving while also introducing you to some of the world's best puzzles.
Thank you for watching!
Simon and Mark

[@coffeedude]

I love it when you show new puzzles!

[@denielsb8010]

Sudoku is what I love and solve daily, but I come here to enjoy everything else but "classic sudoku"! Would love to see 5-10 videos on each new puzzle type/variant! Definetly, not one after another, but in a lovely mix ;)

[@freddiehand6551]

For some time, I was as blind as most to the checkerboard, which made me clueless as to how to approach a cave. However, after learning about the nuances, cave has become one of my favourite puzzles! There is an incredible diversity of strategies.

[@saintjynr]

I actually had never understood properly why the chekerboard pattern wasn't allowed, thinking about the single loop rule really helped

[@fertjuh]

Thanks! Really like the variety in content.

[@sonalita_]

Another way of looking at the double loops is to notice that all the regions connected by x's have to touch an outside edge - so for example if you shaded all the X's yellow, then each patch of yellow must touch an outside edge

[@sabinrawr]

This is the same logic I use for Slitherlink. Those got so much easier once I learned to shade inside/outside regions!

[@user-qi9ei2sz6n]

Whew. Thanks for the checkerboard tip. I’m doing a MASSIVE cave puzzle from Nikoli Puzzlebox 14 and it helped immensely. I might also note something I came up with on my own. I use black squares where you use X’s, but either way it’s interesting to note that all of the black squares must eventually join a side. Furthermore no two strings of black squares can touch. For really big puzzles this is a big help

[@jinbe-san]

I just started trying the daily GAPP puzzles and wanted to look for more cave puzzles to practice, and when I googled, an old CTC video popped up!

[@Ruddigore]

A great tutorial. I spent many months doing hundreds of these cave puzzles and once you get used to them they are easy-peasy. However, when you first start out doing this type of puzzle you must be very, very careful not to double count numbers that contain both rows and columns.

[@jkid1134]

This was nice. It would be nicer to see you do a harder one of these. Also, where can I go to attempt puzzles like this myself? Looks fun!

[@freddiehand6551]

There are many such puzzles at gmpuzzles.com

[@oswaldchangerton5328]

Awesome variant!

[@alandouglas2789]

Can you please do an app with these?

[@alexbaucom17]

So I don't fully understand the loop logic here. The very last checkerboard example he uses at 17:11 highlights my confusion. The rules of the puzzle say to draw a single closed loop around the outside of the shaded region and, with the spot he is at near the end of the video, I could do that and still leave the internal X that he claims is invalid without ever having to lift my pen up and draw a second loop. So is this just a case of the rules being poorly worded or am I not understanding something?

[@freddiehand6551]

It is the words 'closed loop' (and Simon's admittedly slightly misleading explanation) that are confusing you. The definition of a closed loop is a loop which does not intersect itself, even at a corner, so that would be impossible.

[@alexbaucom17]

@@freddiehand6551 Ah I see. Yes that is a much better definition. That makes it much clearer to see why boxes which touch only diagonally are not allowed. Thanks for the explanation!

[@britboy3456]

I assume the US puzzle championship is only for US citizens, is that right? Loving the puzzle content btw! Any idea when we can see a good puzzle solver program like that?

[@freddiehand6551]

No, anyone is allowed to participate, but only US citizens are eligible to be selected for the US puzzle team.

[@Czeckie]

is there an online app to play these? I can only find print outs

[@AmIOrTheOtherCrazy]

translate.googleusercontent.com/translate_c?depth=1&ie=UTF8&langpair=auto%7Cen&rurl=translate.google.com&sp=nmt4&tbb=1&u=www.janko.at/Raetsel/Corral/index.htm&xid=17259,15700023,15700043,15700186,15700191,15700256,15700259&usg=ALkJrhjnQ6JXSsOPTnMvjc1ZE8FFk2NLQg

[@gaffergold]

I was looking too, and I found this app if you happen to have an iPhone. itunes.apple.com/cy/app/bag-puzzle/id1191713366?mt=8

[@freddiehand6551]

George Parsons the puzzles in that app are rather simple and uninteresting I would say. The best puzzles come from puzzle blogs such as gmpuzzles.com

[@Koopan00ba]

Sorry Simon, but the way you approached the puzzle lead to some confused viewers (judging by the comments). After all, similarly to slitherlink, the objective of the puzzle is to draw a loop, and coloring in the squares is merely a helpful tool to get forward. You already drew the actual loop when going through slitherlinks earlier, and I'm wondering why this couldn't have been handled similarly.

[@Koopan00ba]

It's mainly the checkerboard rule that becomes more clear when seeing the actual line.

[@G.Aaron.Fisher]

"over the years" :-D

[@ChonGeeSan]

Can you do a Tic-tac Logic?

[@harleynuthall3340]

"My Almost fails" Continues to fail

[@shane8037]

"Checkerboard logic" doesn't really seem that intuitive, but I guess I can handle these if I just take it as a rule and don't worry about the why behind it.

[@snipegrzywa]

A similar puzzle has the rules better explained when taking about the loop. Remember, he's solving with the shading, but the actual solution is a single line that starts and ends in same spot (and in his solution would follow the outside of the red areas). Therefore, the single line can't revisit a point. So no + or T intersections of the line. The no + is what causes the no checker board rule

[@shane8037]

@@snipegrzywa That makes sense. I think because they called it a "bag" I was thinking of a nice little freehand curvy line and not shading in the actual grid lines.

[@WildAnimalChannel]

This one's kind of easy I think.

[@jumpfok]

What about the 9 in the example? Shouldn't that be a ten? //edit: I counted two rozs of five, so never mind :D

[@Andrewrb15]

No, it's correctly a 9. Count again

[@jumpfok]

@@Andrewrb15 Indeed, I counted two rows of five instead of the individual cells.