Nurikabe

10 Comments

1. Isabel
   Posted January 10, 2010 at 10:14 pm | Permalink

   Not very difficult, but was confused about the rules. Can the white areas touch by the corners?

   Reply
2. nikoli_freak
   Posted January 11, 2010 at 8:29 am | Permalink

   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.

   Reply
3. Isabel
   Posted January 11, 2010 at 11:48 am | Permalink

   Yeah, that’s what I thought, but in that case the puzzle doesn’t have a unique solution.

   Reply
4. nikoli_freak
   Posted January 11, 2010 at 11:18 pm | Permalink

   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.

   Reply
5. nikoli_freak
   Posted January 12, 2010 at 7:35 pm | Permalink

   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.

   Reply
6. Para
   Posted January 15, 2010 at 11:27 pm | Permalink

   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….

   Reply
7. nikoli_freak
   Posted January 22, 2010 at 12:46 am | Permalink

   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?

   Reply
8. nikoli_freak
   Posted January 22, 2010 at 12:50 am | Permalink

   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,,,

   Reply
9. nikoli_freak
   Posted January 22, 2010 at 9:50 am | Permalink

   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 # #

   Reply
10. nikoli_freak
    Posted January 22, 2010 at 9:59 am | Permalink

    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. 🙁

    Reply