find_ocean.rb

=begin

Given

1. An array of strings where "L" indicates land and "W" indicates water,
2. a coordinate marking a starting point in the middle of the ocean

The Challenge:
Find and mark the ocean in the map by changing appropriate W's to O's.
An ocean coordinate is defined to be any coordinate directly adjacent to any other ocean coordinate.

 Example:
 map = [ "LLLLLLLLWW",
         "LLLLLLLWWW",
         "WWWLLLLLWW" ]

 coordinate: [0,9]

RESULT:

[ "LLLLLLLLOO",
  "LLLLLLLOOO",
  "WWWLLLLLOO" ]

More examples:
map = [ "LLWWWWLLWW",
        "LLWLLWWWWW",
        "WWWLLLLLWW" ]

coordinate: [2,8]

RESULT:

[ "LLOOOOLLOO",
  "LLOLLOOOOO",
  "OOOLLLLLOO" ]

coordinate: [1,2]
Same result.

map = [ "LWWWWLLLWW",
        "WWLLWLLWWW",
        "WWWWWWWWWW" ]

coordinate: [0,9]

RESULT:

[ "LOOOOLLLOO",
  "OOLLOLLOOO",
  "OOOOOOOOOO" ]

=end

require 'set'

def find_ocean(map, x, y)
  return unless map[x][y] == 'W'
  map[x][y] = 'O'
  new_ocean_cells = [{x: x, y: y}]

  loop do
    water_cells = Set.new
    new_ocean_cells.each do |cell|
      look_for_water!(map, water_cells, cell[:x], cell[:y])
    end
    break if water_cells.empty?

    water_cells.each do |cell| # Let's make new ocean cells
      map[cell[:x]][cell[:y]] = 'O'
    end
    new_ocean_cells = water_cells.dup
  end

end

def look_for_water!(map, water_cells, x, y)
  water_cells << {x: x - 1, y: y} if x > 0 && map[x - 1] && map[x - 1][y] == 'W'
  water_cells << {x: x + 1, y: y} if map[x + 1] && map[x + 1][y] == 'W'
  water_cells << {x: x, y: y - 1} if y > 0 && map[x][y - 1] == 'W'
  water_cells << {x: x, y: y + 1} if map[x][y + 1] == 'W'
end

map = [ "LLLLLLLLWW",
        "LLLLLLLWWW",
        "WWWLLLLLWW" ]

find_ocean(map, 0, 9)

map.each{|x| puts x }