The shading of R4C8 is wrong as it isolates the bit of wall below it. It's due to a miscount of yellow cells needed to fulfill the 5 in R1C8. It didn't seem to affect the rest of the solve in any way though.
Somehow I made this exact same error, and I didn't watch the video until I was done with my solve! I only noticed when I read this comment and looked at my completed grid. Strange coincidence!
I noticed now (after doing the puzzle in 30 minutes) I did miscolour r8c9. And that definitely had an impact on the placing of the non-cave digit at the end. 😞
A lot of people failing to realise there's a difference between "shade some cells to LEAVE BEHIND a single connected group" and "shade some cells to FORM a single connected group". It's the unshaded cells left behind that form the cave. (Yellow in Mark's solve).
41:56 - Mark deduces the location of the 1 in row 4 based on the miscoloured r4c8. The clean way of placing it in r4c3 is by placing the 1 in column 4 first, which removes all placement alternatives for 1 in box 4.
Thanks for the birthday wishes and the feature! A few people have mentioned below but anti-checkerboard also applies in cave which helps a lot around the 8 and 21 cages. Well done for getting there without using that information!
Cave, like yin-yang, cannot have a checkerboard pattern. (Cave is equivalent to a yin-yang with an extra border that's all wall.) Using the no-checkerboard strategy helps disambiguate the 35 pair in box 8, and also simplifies reasoning about the W-shaped cage.
Mark never did catch on with the 'whoops' for the coloring on r4c8, whoops. 😅 Something else that would have helped him was knowing that like yin-yang, cave puzzles can never have a checkerboard pattern (but can have 2x2s), which probably would have sped his solve up significantly. My own time was 29:55 (conflict checker off), many thanks to Stephen for the amazing puzzle (and also a Happy Birthday to him)!
I think this is the most horribly worded cave ruleset I've seen so far. Also the cave cell definition does not specify that this total number of cells should only count cave cells...
so many puzzles these days are so horribly worded. i feel like sometimes people go for brevity at the cost of getting the point across comprehensively.
@@distractmeHow is it worded wrong? Seemed fine to me. Although a number of people appear to have missed that it's the cells left behind by the shading that form the cave, ie. the unshaded cells are the cave.
I did, if I really concentrated on it, hear a tiny bit of roaring, but by no means obvious (and had you not mentioned it, I might not really have noticed). Thanks for doing a video for us, Mark, despite being holed up in some non-party part of your house!
The cave is not possible to define precisely as the rules state that all shaded cells need to connect orthoganally to a border. They say nothing about the non cave cells. Mark makes an error in shading columns 7, and 9. I cannot see any reason why the 9 in box 3 cannot descend to row 8 and end in colmn 8 OR descend to row 7 and and get to row 7. Either seems equally valid. Thus when I had a 17 pair in clumn 8 rows 1 and 2 I could find no way of disambiguating them, so at that point I guessed one way and it concluded that I was right. I then returned and guessed the other way and it got very messy and ambiguous. Am I missing something?
I looked at the solution to make sure I had the rules right, and had a minor epiphany. The goal of sudoku isn't to produce a completed puzzle; rather, it's to discover a sequence of logical steps that produces one. That's why guessing and bifurcation are frowned upon.
I think the rules in the linked puzzle have a problem. They only state that shaded cells must be connected to each other and say nothing about unshaded cells. But unless you understand that unshaded cells must all have a connection to the edge of the grid, the puzzle doesn't have a unique solution. Am I missing something?
"Shade some cells to leave behind a single connected group - the cave". The cells you leave behind are the unshaded cells. These are the cells Mark colours yellow. They have to be a "single connected group". Further, there must be "no enclosed, shaded cells". Shaded cells are grey in Mark's solve. These must not be enclosed, so they must connect to the edge of the grid "(ie. all shaded cells must be connected by other shaded cells to an edge of the grid)".
Shaded cells are (in the instructions) the wall. “... with no enclosed, shaded cells. (I.e. all shaded cells must be connected by other shaded cells to an edge of the grid). But I had to read this at least 5 times before fully understanding it...
Not happy with the way the rules are written. My initial interpretation meant that although cave cells must connect to the edge, non cave cells need not connect to the edge. Because the instructions say to shade cave cells, and shaded cells must touch the edge and must not be enclosed. But never says to shade non caves, I assumed non caves could be enclosed. It added a good 40 min to my solve time.
"Shade some cells to LEAVE BEHIND a single connected group - the cave". It's the unshaded cells (Mark colours yellow) left behind that form the cave. They do not have to connect to the edge of the grid (but not unsurprisingly, they do). They just all have to be connected. It's the shaded cells (grey in Mark's solve) that cannot be enclosed, so have to reach the edge of the grid.
Yeah. He forgot to count the corner cell. But you can reach the same conclusion by realising that R4C8 has to be grey so that the grey wall can escape to the edge, which then forces R1C7 to be yellow.
@@vicstick75The rules only asked for shades cells (yellow) to be connected to edge. It says nothing about the unshaded cells (grey) though. Horribly worded rules.
@@bihoulaw9937other way round. Yellow are cave and must all interconnect; grey are the cave walls and don't all need to interconnect, but must touch the edges.
"no enclosed, shaded cells" Also, to clarify that, "(ie. all shaded cells must be connected by other shaded cells to an edge of the grid)". So it says it twice.
@@johnhumberstone9674 No. That seems to be a common misunderstanding reading through the comments. The cave cells are the cells LEFT BEHIND, so the unshaded cells (yellow in Mark's solve). The shaded cells are the walls (grey in Mark's solve).
Screaming about miscoloring r4c8. That is later used to say that 1 has to be in r4c3 because that is the only gray cell left in row 4. Also also screaming about not allowing checkerboard patterns!
Doesn't 1 *have* to be the naughty digit from the very start? If I read the rules right, a 1 would be a solo box, disconnected from the rest of the grid. Right?
@@GreatUSTreasureHunt Yeah, I found this puzzle's ruleset hard to understand. Usually I can just read it and understand what they mean, but this time I needed the explanation.
Unlike Simon, Mark is not patient to clarify and illustrate complex rulesets. We have to watch a few minutes of his solve in order to understand the ruleset.
I'm ten minutes in and wondering whether Mark finds a way to solve it without referencing "no checkerboards". Let's find out ... Edit: OMG. HE'S ONLY GONE AND DONE IT!!! (Well, if he could count to 5 in box 3 he would have). Mark solving on hard mode. 😂
It's not yin-yang. Cave is different - it has different rules for coloring than yin-yang. (He does make a small mistake in coloring, but not because he did not follow yin-yang rules, since they don't apply in this puzzle.)
@@emilywilliams3237It does share the "no checkerboards" restriction with Yin-Yang style puzzles though, and Mark overlooked it. Simon would have been all over it. No checkerboarding would have shaded r7c5 grey and sorted out the 3,5 cage order much earlier. That in turn would have sorted out the 4,5 cage order, and led to a much smoother solution path. He did make other counting errors too, that slowed down his solve. E.g. looking at what happened if he made r2c3 yellow at 27:45, which made the two cage cells in the 21 box see at least SIX cave cells already, and break. He almost made a couple of other errors, but fortunately caught them himself (8:30 and 20:59). I don't think this was one of Mark's better days. Possibly because he's trying to solve it quickly so he can return to the party, and before he gets interrupted by the return of the noisy teenage boys. 🙂
This is a horribly written ruleset that when actually followed as written is impossible from the very start. I can't even begin to solve it, because the rules as written are simply wrong. Fix the rules. Make it actually solvable without having to guess what the puzzle-setter intended instead of what they wrote down (which is utter nonsense)
How are they impossible? The rules state it's the cells LEFT BEHIND that are the cave, i.e. the unshaded cells form a single connected region - the cave. The shaded cells are the walls of the cave, and they cannot be enclosed, meaning they have to reach the edge of the grid. I read the rules and solved the puzzle even without watching Mark's introduction, so clearly not impossible.
@@RichSmith77 The rules say that ' "cave clues" must be a part of the cave, with each number indicating the total count of cells connected vertically and horizontally to the numbered cell including the cell itself. Total count of cells "connected vertically and horizontally to the numbered cell". Not "cave cells" only, not "cave cells visible to them vertically and horizontally" but rather "total count of cells connected vertically and horizontally. By that rule cage cells ought have "2" if they're at the corner of the diagram (corner cells have 2 cells connected horizontally and vertically), "3" if they're at the edge of the diagram (edge cells have 3 cells they connect to horizontally and vertically), and "4" if they're at neither the corner nor the edge of the diagram (rest of the cells have 4 cells they connect to horizontally and verticalyly). That is impossible because then r9c7 and r9c8 ought both have a '3' in them and that violates Sudoku. Instead the solution has digits like 7 because the ACTUAL REAL rules means how many CAVE CELLS are VISIBLE to the cell in question (horizontally and vertically assuming walls block vision), not the "total count of cells" (ANY CELLS, since CAVE CELLS are not specified) and not "connected",. The rules as stated are false. You didn't solve the problem following the rules given here, you solved the problem by knowing the better-stated rulesets of OTHER puzzles.
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The shading of R4C8 is wrong as it isolates the bit of wall below it. It's due to a miscount of yellow cells needed to fulfill the 5 in R1C8. It didn't seem to affect the rest of the solve in any way though.
Noticed the error too but it was a great solve as always
Somehow I made this exact same error, and I didn't watch the video until I was done with my solve! I only noticed when I read this comment and looked at my completed grid. Strange coincidence!
He uses that being yellow to say that 1 has to be in r4c3 as that was the last gray cell in that row.
I noticed now (after doing the puzzle in 30 minutes) I did miscolour r8c9. And that definitely had an impact on the placing of the non-cave digit at the end. 😞
I noticed the incorrect shading as well in his solve but since he had the correct digit in r1c8 then it didn’t affect the solve
Yes, be careful not to confuse Nick Cave with Nic Cage.
Naughty, naughty, Mark, no checkerboarding.
A lot of people failing to realise there's a difference between "shade some cells to LEAVE BEHIND a single connected group" and "shade some cells to FORM a single connected group".
It's the unshaded cells left behind that form the cave. (Yellow in Mark's solve).
00:34:05 for me. Loved this puzzle! Well done Stephen! Kind comment.
Thank you!
41:56 - Mark deduces the location of the 1 in row 4 based on the miscoloured r4c8. The clean way of placing it in r4c3 is by placing the 1 in column 4 first, which removes all placement alternatives for 1 in box 4.
If anyone is wondering, the 1's in rows 4,5,6 could be solved by 38 minutes in without the error
Thanks for the birthday wishes and the feature! A few people have mentioned below but anti-checkerboard also applies in cave which helps a lot around the 8 and 21 cages. Well done for getting there without using that information!
Cave, like yin-yang, cannot have a checkerboard pattern. (Cave is equivalent to a yin-yang with an extra border that's all wall.)
Using the no-checkerboard strategy helps disambiguate the 35 pair in box 8, and also simplifies reasoning about the W-shaped cage.
Mark never did catch on with the 'whoops' for the coloring on r4c8, whoops. 😅 Something else that would have helped him was knowing that like yin-yang, cave puzzles can never have a checkerboard pattern (but can have 2x2s), which probably would have sped his solve up significantly.
My own time was 29:55 (conflict checker off), many thanks to Stephen for the amazing puzzle (and also a Happy Birthday to him)!
Thank you very much!
He should also have noted the isolated wall cells in box 6 that can no longer connect to the edge.
34:03 ... I do like these 'cave' sudokus, even if I don't always figure everything out (which was *not* the case for me today)
Nice puzzle!
Thank you :)
I didn't even understand the rules.
I think this is the most horribly worded cave ruleset I've seen so far. Also the cave cell definition does not specify that this total number of cells should only count cave cells...
Didn't seem bad to me. Also Mark explains it so 🤷@@mxj3287
so many puzzles these days are so horribly worded. i feel like sometimes people go for brevity at the cost of getting the point across comprehensively.
@@mxj3287 Its also worded wrong on the text, both on the sudokupad and on this video and description
@@distractmeHow is it worded wrong? Seemed fine to me. Although a number of people appear to have missed that it's the cells left behind by the shading that form the cave, ie. the unshaded cells are the cave.
I did, if I really concentrated on it, hear a tiny bit of roaring, but by no means obvious (and had you not mentioned it, I might not really have noticed). Thanks for doing a video for us, Mark, despite being holed up in some non-party part of your house!
21:58 finish. A very nice, straightforward puzzle. Fun!
Thanks :)
The cave is not possible to define precisely as the rules state that all shaded cells need to connect orthoganally to a border. They say nothing about the non cave cells.
Mark makes an error in shading columns 7, and 9.
I cannot see any reason why the 9 in box 3 cannot descend to row 8 and end in colmn 8 OR descend to row 7 and and get to row 7. Either seems equally valid.
Thus when I had a 17 pair in clumn 8 rows 1 and 2 I could find no way of disambiguating them, so at that point I guessed one way and it concluded that I was right. I then returned and guessed the other way and it got very messy and ambiguous.
Am I missing something?
Colouring is wrong as long as cave puzzles cannot contain "checkerboards". Anz 17 in column 8 are "hanging" shaded cells.
I looked at the solution to make sure I had the rules right, and had a minor epiphany. The goal of sudoku isn't to produce a completed puzzle; rather, it's to discover a sequence of logical steps that produces one. That's why guessing and bifurcation are frowned upon.
11:52 - Does Mark ever realise that he marked r4c8 as yellow when it should be grey?
nope.
Probably, when he came to read the comments. Might mention it in tomorrow's video.
I think the rules in the linked puzzle have a problem. They only state that shaded cells must be connected to each other and say nothing about unshaded cells. But unless you understand that unshaded cells must all have a connection to the edge of the grid, the puzzle doesn't have a unique solution. Am I missing something?
"Shade some cells to leave behind a single connected group - the cave". The cells you leave behind are the unshaded cells. These are the cells Mark colours yellow. They have to be a "single connected group".
Further, there must be "no enclosed, shaded cells". Shaded cells are grey in Mark's solve. These must not be enclosed, so they must connect to the edge of the grid "(ie. all shaded cells must be connected by other shaded cells to an edge of the grid)".
@@RichSmith77 ah, the key word is "behind"! I glossed over it. Thank you!
@@rentalcustard Reading through the comments, you're not alone. Seems to have confused a few people.
Shaded cells are (in the instructions) the wall. “... with no enclosed, shaded cells. (I.e. all shaded cells must be connected by other shaded cells to an edge of the grid).
But I had to read this at least 5 times before fully understanding it...
Not happy with the way the rules are written. My initial interpretation meant that although cave cells must connect to the edge, non cave cells need not connect to the edge. Because the instructions say to shade cave cells, and shaded cells must touch the edge and must not be enclosed. But never says to shade non caves, I assumed non caves could be enclosed. It added a good 40 min to my solve time.
"Shade some cells to LEAVE BEHIND a single connected group - the cave". It's the unshaded cells (Mark colours yellow) left behind that form the cave. They do not have to connect to the edge of the grid (but not unsurprisingly, they do). They just all have to be connected.
It's the shaded cells (grey in Mark's solve) that cannot be enclosed, so have to reach the edge of the grid.
There is a mistake at 11:52 in the video
Yeah. He forgot to count the corner cell. But you can reach the same conclusion by realising that R4C8 has to be grey so that the grey wall can escape to the edge, which then forces R1C7 to be yellow.
@@vicstick75The rules only asked for shades cells (yellow) to be connected to edge. It says nothing about the unshaded cells (grey) though. Horribly worded rules.
@@bihoulaw9937Yellow are the cave cells. Grey are the shaded wall cells. Grey does have to reach the edge
@@bihoulaw9937other way round. Yellow are cave and must all interconnect; grey are the cave walls and don't all need to interconnect, but must touch the edges.
Where does it say that walls have to get to the edge of the grid at 5 minutes?
"no enclosed, shaded cells"
Also, to clarify that, "(ie. all shaded cells must be connected by other shaded cells to an edge of the grid)".
So it says it twice.
@@RichSmith77 The walls are unshaded.
@@johnhumberstone9674 No. That seems to be a common misunderstanding reading through the comments. The cave cells are the cells LEFT BEHIND, so the unshaded cells (yellow in Mark's solve). The shaded cells are the walls (grey in Mark's solve).
Screaming about miscoloring r4c8. That is later used to say that 1 has to be in r4c3 because that is the only gray cell left in row 4.
Also also screaming about not allowing checkerboard patterns!
Rules on the puzzle are wrong - don't mention anything about unshaded cells!
"Shade some cells to leave behind a single connected group - the cave".
The cells you "leave behind" are the unshaded cells, clearly.
Doesn't 1 *have* to be the naughty digit from the very start? If I read the rules right, a 1 would be a solo box, disconnected from the rest of the grid. Right?
1 can't go in the cages, which doesn't necessarily mean it can't go in the cave cells that aren't in cages.
@@compiling Understood. Thanks.
Sometimes these rules sets are more difficult than the puzzle itself.
@@GreatUSTreasureHunt Yeah, I found this puzzle's ruleset hard to understand. Usually I can just read it and understand what they mean, but this time I needed the explanation.
Unlike Simon, Mark is not patient to clarify and illustrate complex rulesets. We have to watch a few minutes of his solve in order to understand the ruleset.
And once again Mark has submitted an incorrect solution.
I'm ten minutes in and wondering whether Mark finds a way to solve it without referencing "no checkerboards". Let's find out ...
Edit: OMG. HE'S ONLY GONE AND DONE IT!!! (Well, if he could count to 5 in box 3 he would have). Mark solving on hard mode. 😂
word salad rules
49:12 for me.
47:47 for me and solver #1040.
25:58 for me. not that hard.
Mark was not joking when he said he was not good at ying-yang. He made so many mistakes here.
It's not yin-yang. Cave is different - it has different rules for coloring than yin-yang. (He does make a small mistake in coloring, but not because he did not follow yin-yang rules, since they don't apply in this puzzle.)
@@emilywilliams3237It does share the "no checkerboards" restriction with Yin-Yang style puzzles though, and Mark overlooked it. Simon would have been all over it. No checkerboarding would have shaded r7c5 grey and sorted out the 3,5 cage order much earlier. That in turn would have sorted out the 4,5 cage order, and led to a much smoother solution path.
He did make other counting errors too, that slowed down his solve. E.g. looking at what happened if he made r2c3 yellow at 27:45, which made the two cage cells in the 21 box see at least SIX cave cells already, and break.
He almost made a couple of other errors, but fortunately caught them himself (8:30 and 20:59).
I don't think this was one of Mark's better days. Possibly because he's trying to solve it quickly so he can return to the party, and before he gets interrupted by the return of the noisy teenage boys. 🙂
This is a horribly written ruleset that when actually followed as written is impossible from the very start. I can't even begin to solve it, because the rules as written are simply wrong.
Fix the rules. Make it actually solvable without having to guess what the puzzle-setter intended instead of what they wrote down (which is utter nonsense)
How are they impossible?
The rules state it's the cells LEFT BEHIND that are the cave, i.e. the unshaded cells form a single connected region - the cave. The shaded cells are the walls of the cave, and they cannot be enclosed, meaning they have to reach the edge of the grid.
I read the rules and solved the puzzle even without watching Mark's introduction, so clearly not impossible.
@@RichSmith77 The rules say that ' "cave clues" must be a part of the cave, with each number indicating the total count of cells connected vertically and horizontally to the numbered cell including the cell itself.
Total count of cells "connected vertically and horizontally to the numbered cell".
Not "cave cells" only, not "cave cells visible to them vertically and horizontally" but rather "total count of cells connected vertically and horizontally.
By that rule cage cells ought have "2" if they're at the corner of the diagram (corner cells have 2 cells connected horizontally and vertically), "3" if they're at the edge of the diagram (edge cells have 3 cells they connect to horizontally and vertically), and "4" if they're at neither the corner nor the edge of the diagram (rest of the cells have 4 cells they connect to horizontally and verticalyly). That is impossible because then r9c7 and r9c8 ought both have a '3' in them and that violates Sudoku.
Instead the solution has digits like 7 because the ACTUAL REAL rules means how many CAVE CELLS are VISIBLE to the cell in question (horizontally and vertically assuming walls block vision), not the "total count of cells" (ANY CELLS, since CAVE CELLS are not specified) and not "connected",.
The rules as stated are false. You didn't solve the problem following the rules given here, you solved the problem by knowing the better-stated rulesets of OTHER puzzles.
First post! This looks like a fun one!