Nurikabe 10×10 (difficult?)
As you may have noticed, I’ve changed things a little on the site, by removing some of the daily puzzles. While Daily Killer Sudoku and Daily Sudoku variation will remain, as well as bi-Weekly Samurai Sudoku, all other puzzles will be posted here, on the main page of the site. Expect at least a couple of puzzles every week, if not more. All sorts of puzzles will be posted, with no particular schedule.
So, next up is Nurikabe. I’ve only ever posted one of them and I’m still working on determining the difficulty of them, so please let me know how difficult you find them.
If you are uncertain about the rules of Nurikabe, read my Nurikabe introductory article.
Nurikabe 10×10 for January 8, 2010
Click to download the puzzle in your favorite format:
Cheers!
January 10th, 2010 at 10:14 pm
Not very difficult, but was confused about the rules. Can the white areas touch by the corners?
January 11th, 2010 at 8:29 am
The white areas can touch diagonally.
Check out the example solution on the wikipedia page:
http://en.wikipedia.org/wiki/Nurikabe
Another important point is each white area contains one and only one number.
You cannot create a white area out of blank cells, and you cannot join 2 numbers into a single white area.
January 11th, 2010 at 11:48 am
Yeah, that’s what I thought, but in that case the puzzle doesn’t have a unique solution.
January 11th, 2010 at 11:18 pm
Which puzzle?
They all have unique solutions to me.
If you believe a puzzle have multiple solutions, just post at least 2 of them out, and see if others can point out if you have made a mistake.
January 12th, 2010 at 7:35 pm
Isabel
Good, I guess the lack of reply means you have spot your mistake and realise the solution for this puzzle is unique:
#40###0###
##0#2#3#0#
6#0#0#0#0#
0#######0#
0#2#0#3#4#
0#0#2#0###
0#####0#0#
0#003###0#
######0#3#
#02#004###
It is just a coincidence that all the white areas in the solution do not touch diagonally.
If you found other solutions with diagonally touching white areas, they are certain to violate the rules, one way or the other.
January 15th, 2010 at 11:27 pm
This puzzle isn’t that hard. The problem mainly is that it is too minimal. It works only on the fact that the islands will only fit one way so that there aren’t any 2×2 areas anywhere. What makes Nurikabes harder is when there is only one way that all the water can connect AND there are no 2×2 areas anywhere. At least that is my opinion.
Compare it for example to this 9×9 nurikabe I made.
…..4…
………
….7….
2..5…..
……3..
………
…….4.
…6…..
….3….
January 22nd, 2010 at 12:46 am
Para
Thank you for the 9×9 nurikabe. I think it makes a very hard puzzle for most players. Especially those who are not familiar with Nikoli puzzles.
Here is what I think makes the hardest step:
####-400-
#00–##-#
##D#70—
2–5#-#–
-#–C-3–
#-AB—–
#——4-
#0-6#-#–
####30—
From this position, to ‘grow’ the white area for the 5-clue, it must include A,B,C or D.
It cannot include A or B because that would ‘link’ the 5-clue and 6-clue diagonally, and that in turn would prevent the black cells from being connected together in one piece.
It cannot include C because it would very quickly force the 4 cells in rows 2 & 3, columns 8 & 9 to be unreachable from all number clues, thus creating a 2×2 black area.
So the 5-clue must ‘link’ to D and also the 2 determined white cells above, and the whole white area for the 5-clue is determined, and the puzzle becomes very easy from that step.
I wonder does anyone have a better way to solve it?
January 22nd, 2010 at 12:50 am
I don’t know why, but in my grid some groups of short dashes are automatically changed to long dashes.
Here is another grid (with commas replacing dashes to represent unsolved cells):
####,400,
#00,,##,#
##D#70,,,
2,,5#,#,,
,#,,C,3,,
#,AB,,,,,
#,,,,,,4,
#0,6#,#,,
####30,,,
January 22nd, 2010 at 9:50 am
Equal signs –> unsolved cells
Hash signs –> black cells
Zeros (and numbers) –> white cells
# # # # = 4 0 0 =
# 0 0 = = # # = #
# # D # 7 0 = = =
2 = = 5 # = # = =
= # = = C = 3 = =
# = A B = = = = =
# = = = = = = 4 =
# 0 = 6 # = # = =
# # # # 3 0 = = =
Solution:
# # # # 0 4 0 0 #
# 0 0 # # # # # #
# # 0 # 7 0 0 0 0
2 # 0 5 # # # # 0
0 # # # 0 0 3 # 0
# # 0 # # # # # #
# 0 0 0 # 0 0 4 #
# 0 # 6 # # # 0 #
# # # # 3 0 0 # #
January 22nd, 2010 at 9:59 am
Last try, using underscores for unsolved cells
# # # # _ 4 0 0 _
# 0 0 _ _ # # _ #
# # D # 7 0 _ _ _
2 _ _ 5 # _ # _ _
_ # _ _ C _ 3 _ _
# _ A B _ _ _ _ _
# _ _ _ _ _ _ 4 _
# 0 _ 6 # _ # _ _
# # # # 3 0 _ _ _
Sorry for so many tries. It would be nice to have a ‘preview’ feature when posting.