[RUBY] Rails on Tiles (how to write)


The problem is finding a route that goes out of range when moving along the rails of a given tile.


module RailsOnTiles
  Tiles = [[2, 3, 0, 1], [1, 0, 3, 2], [3, 2, 1, 0]]
  Dirs = [[0, -1], [1, 0], [0, 1], [-1, 0]]
  def go(input)
    field = input.chars.map(&:to_i).each_slice(3).to_a
    solve(field).map { |i| ("A".."I").to_a[i] }.join
  def solve(field, x=1, y=-1, dir=2, route=[])
    dx, dy = Dirs[dir]
    x += dx
    y += dy
    return route if x < 0 || x > 2 || y < 0 || y > 2
    rev = Tiles[0][dir]
    nxt = Tiles[field[y][x]][rev]
    tile_num = y * 3 + x
    solve(field, x, y, nxt, route + [tile_num])

if __FILE__ == $0
  require 'minitest/autorun'
  describe 'RailsOnTiles' do
      ["101221102", "BEDGHIFEH"],
      ["000000000", "BEH"],
      ["111111111", "BCF"],
      ["222222222", "BAD"],
      ["000211112", "BEFIHEDGH"],
      ["221011102", "BADGHIFEBCF"],
      ["201100112", "BEHIFCBADEF"],
      ["000111222", "BEFIH"],
      ["012012012", "BC"],
      ["201120111", "BEDABCFI"],
      ["220111122", "BADEHGD"],
      ["221011022", "BADG"],
      ["111000112", "BCFIHEBA"],
      ["001211001", "BEFI"],
      ["111222012", "BCFEHIF"],
      ["220111211", "BADEHI"],
      ["211212212", "BCFEBAD"],
      ["002112210", "BEFC"],
      ["001010221", "BEF"],
      ["100211002", "BEFIHG"],
      ["201212121", "BEFCBAD"]
    ].each do |input, expect|
      it input do
        assert_equal RailsOnTiles.go(input), expect 

field represents the arrangement of tiles, and the tile type is stored in Tiles. As for the direction type, 0,1,2,3 represent the upper right lower left respectively. If you go down from the previous tile, the next tile will "reverse" so that it comes from the top, so it goes into rev. After that, it recurses until it goes out of field and returns the result.

In addition, since the route route represents the position of the tile with a number, it is converted to the alphabet at the end.

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