14 Ruby

# init large enough 2D array, fill with spaces
map = Array.new(1000){Array.new(1000," ")}
maxcol = 0
maxrow = 0

# printing of the map with sand for debugging
def print_map(map, maxrow, maxcol)
  for i in 0..maxrow do
    # print only the interesting part of map
    for j in 300..maxcol do
      # sand source
      if j == 500 and i == 0
        print "X"
      # rock
      elsif map[i][j] == '#'
        print map[i][j]
      # sand
      elsif map[i][j] == 'o'
        print map[i][j]
      # empty space
      else
        print " "
      end
    end
    # print doesn't print newline by default
    print "\n"
  end
end

# parse input and obtain the map
File.readlines('14.input').each do |line|
  # remember the last coordinates
  # within a line
  # so we can draw lines between pairs
  prev_row = nil
  prev_col = nil
  # split by spaces and process tokens
  line.split(" ").each do |token|
    if token.include? ","
      # num1,num2 => split into two integers
      col_s, row_s = token.split(",")
      col = col_s.to_i # string to integer
      row = row_s.to_i
      # search for the maximum column
      if col > maxcol
        maxcol = col
      end
      # search for the maximum row
      if row > maxrow
        maxrow = row
      end
      # horizontal line of rock
      if prev_row == row
        # prev_col -> col
        if prev_col < col
          for i in prev_col..col do
            map[row][i] = "#"
          end
        else
          # also prev_col <- col
          for i in col..prev_col do
            map[row][i] = "#"
          end
        end
      end
      # vertical line of rock
      if prev_col == col
        if prev_row < row
          for i in prev_row..row do
            map[i][col] = "#"
          end
        else
          for i in row..prev_row do
            map[i][col] = "#"
          end
        end
      end
      # update the previous coordinates
      prev_row = row
      prev_col = col
    end
  end
end

# count of sand (grains?)
count = 0
# sand is produced at (0,500)
x = 500
y = 0
# add sand on the map
map[y][x] = 'o'

# loop forever (just for now)
while true do
  # sand has fallen under the radar
  # should be maxrow instead of map.length
  # but it doesn't matter here
  # stop looping and report the sand count
  if y == map.length - 1
    print "Abbyss! Count: ", count, "\n"
    break
  end
  # decide where sand goes
  # if sand or rock is below
  if map[y+1][x] == '#' or map[y+1][x] == 'o'
    # if we can slide to the left
    if map[y+1][x-1] == ' '
      # move the sand on the map and update
      # its position
      map[y][x] = ' '
      x -= 1
      y += 1
      map[y][x] = 'o'
    # or move to the right
    elsif map[y+1][x+1] == ' '
      # update position
      map[y][x] = ' '
      x += 1
      y += 1
      map[y][x] = 'o'
    # sand will stay here
    else
      # produce new sand
      x = 500
      y = 0
      # count it in and continue
      count += 1
    end
  # can fall down
  else
    # update coordinates and sand in map
    map[y][x] = ' '
    y += 1
    map[y][x] = 'o'
  end
end

map = Array.new(1000){Array.new(1000," ")}
maxcol = 0
maxrow = 0

File.readlines('14.input').each do |line|
  prev_row = nil
  prev_col = nil
  line.split(" ").each do |token|
    if token.include? ","
      col_s, row_s = token.split(",")
      col = col_s.to_i
      row = row_s.to_i
      if col > maxcol
        maxcol = col
      end
      if row > maxrow
        maxrow = row
      end
      if prev_row == row
        if prev_col < col
          for i in prev_col..col do
            map[row][i] = "#"
          end
        else
          for i in col..prev_col do
            map[row][i] = "#"
          end
        end
      end
      if prev_col == col
        if prev_row < row
          for i in prev_row..row do
            map[i][col] = "#"
          end
        else
          for i in row..prev_row do
            map[i][col] = "#"
          end
        end
      end
      prev_row = row
      prev_col = col
    end
  end
end

# add the rock bottom, enlarge to the right
# to make space for the big sand pile
maxrow += 2
for i in 0..(maxcol+200) do
  map[maxrow][i] = "#"
end

count = 0
x = 500
y = 0
map[y][x] = 'o'

while true do
  if y == maxrow
    # start with new sand
    x = 500
    y = 0
    map[y][x] = 'o'
    count += 1
  end
  if map[y+1][x] == '#' or map[y+1][x] == 'o'
    if map[y+1][x-1] == ' '
      map[y][x] = ' '
      x -= 1
      y += 1
      map[y][x] = 'o'
    elsif map[y+1][x+1] == ' '
      map[y][x] = ' '
      x += 1
      y += 1
      map[y][x] = 'o'
    else
      # if we stay and are at the sand source
      # position we know we are full
      if x == 500 and y == 0
        count += 1
        # report count
        print "Filled to top ", count, "\n"
        break
      end
      x = 500
      y = 0
      map[y][x] = 'o'
      count += 1
    end
  else
    map[y][x] = ' '
    y += 1
    map[y][x] = 'o'
  end
end