From: Phrogz <phrogz@...>
Date: 2008-05-06T12:40:05+09:00
Subject: Re: Help with array

On May 5, 1:06 pm, Victor Reyes <victor.re...@gmail.com> wrote:
> Given a multidimensional array (9x9) I am trying to inspect each row and
> each column as follows:
> I can do this with some ugly looking and probably inefficient loop. However,
> Ruby has so many tools and "tricks" that perhaps there might be some way of
> doing this quicker and easy to understand.

I don't think there's any way to do this without looking at every
cell. I was a little confused by your massive amount of text, so I
assume you're saying that each cell has more than one number in it.
(As occurs when writing down possibilities.)

Following is a simple iteration that will go through every cell and,
in a single pass, update the count of instances of a particular digit
in each row and column. I've implemented the multiple-numbers-per-cell
as an array per cell. If you have a string...well, don't do that,
because it'd be silly. :)

Hope this helps you with some insight into Ruby. As I'm offering this
code up to a newbie to learn from, others please feel free to post
followups ripping it apart and suggesting better ways to accomplish
the same goals.

# Create a 9x9 array, where each cell is an empty array
cells = Array.new(9){
  Array.new(9){ [] }
}

# Fill each cell with dummy data (not sudoku-ready)
# of zero or more integers
cells.each{ |row|
  row.each{ |cell|
    1.upto(9){ |i|
      # 20% chance of each number in some cell leaves
      # us with a 13% chance of no numbers per cell.
      # There's thus a 99.999% chance that at least one
      # cell will be left empty (if my math is correct)
      cell << i if rand < 0.2
    }
  }
}

# Now run through all the cells and count numbers
nums_by_row = Array.new(9){ Hash.new(0) }
nums_by_col = Array.new(9){ Hash.new(0) }
cells.each_with_index{ |row, row_num|
  row.each_with_index{ |cell, col_num|
    cell.each{ |num|
      nums_by_row[ row_num ][ num ] += 1
      nums_by_col[ col_num ][ num ] += 1
    }
  }
}

# Following output hand-formatted for clarity
# Beware unfortunate line-wrapping

p cells
# [
#  [[1,3,6,7,9], [2,9], [1,8], [1,4], [1,6], [1], [7], [2,3,5,9],
[8]],
#  [[2,3], [], [6,7], [5], [4,5,6,7,8,9], [2,5], [2,3,4], [7,9], []],
#  [[4], [3,4], [], [], [5,7], [1,2,5,6], [3,4], [2], [2,4,8]],
#  [[2,5], [7], [3,5,6,8,9], [], [3,7], [1,5,8], [1,2,4], [2], [3]],
#  [[4,5], [4,8], [6], [], [4], [], [9], [4,6], [7,8]],
#  [[3,4,6,9], [6], [9], [4,7], [2,9], [2,3,5,9], [4], [2,5,9], [9]],
#  [[8], [5], [2,7], [], [5], [6,7], [3,4,7,9], [4,5], [4,5,6]],
#  [[7,9], [], [], [2], [7,8,9], [3,7,9], [], [], [6,7]],
#  [[3], [5], [4,7], [1,2,5], [2,3,6,7,8], [1,3,5,8,9], [4,6], [],
[5]]
# ]

p nums_by_row
# [{1=>5, 2=>2, 3=>2, 4=>1, 5=>1, 6=>2, 7=>2, 8=>2, 9=>3},
#  {      2=>3, 3=>2, 4=>2, 5=>3, 6=>2, 7=>3, 8=>1, 9=>2},
#  {1=>1, 2=>3, 3=>2, 4=>4, 5=>2, 6=>1, 7=>1, 8=>1      },
#  {1=>2, 2=>3, 3=>3, 4=>1, 5=>3, 6=>1, 7=>2, 8=>2, 9=>1},
#  {                  4=>4, 5=>1, 6=>2, 7=>1, 8=>2, 9=>1},
#  {      2=>3, 3=>2, 4=>3, 5=>2, 6=>2, 7=>1,       9=>6},
#  {      2=>1, 3=>1, 4=>3, 5=>4, 6=>2, 7=>3, 8=>1, 9=>1},
#  {      2=>1, 3=>1,             6=>1, 7=>4, 8=>1, 9=>3},
#  {1=>2, 2=>2, 3=>3, 4=>2, 5=>4, 6=>2, 7=>2, 8=>2, 9=>1}]

p nums_by_col
# [{1=>1, 2=>2, 3=>4, 4=>3, 5=>2, 6=>2, 7=>2, 8=>1, 9=>3},
#  {      2=>1, 3=>1, 4=>2, 5=>2, 6=>1, 7=>1, 8=>1, 9=>1},
#  {1=>1, 2=>1, 3=>1, 4=>1, 5=>1, 6=>3, 7=>3, 8=>2, 9=>2},
#  {1=>2, 2=>2,       4=>2, 5=>2,       7=>1            },
#  {1=>1, 2=>2, 3=>2, 4=>2, 5=>3, 6=>3, 7=>5, 8=>3, 9=>3},
#  {1=>4, 2=>3, 3=>3,       5=>5, 6=>2, 7=>2, 8=>2, 9=>3},
#  {1=>1, 2=>2, 3=>3, 4=>6,       6=>1, 7=>2,       9=>2},
#  {2=>4, 3=>1, 4=>2, 5=>3,       6=>1, 7=>1,       9=>3},
#  {2=>1, 3=>1, 4=>2, 5=>2,       6=>2, 7=>2, 8=>3, 9=>1}]