13.rb

#!/usr/bin/env ruby

require 'pp'
puts 'hi'

GRID_SIZE = 250
FILENAME = 'input.txt'
#GRID_SIZE = 13
#FILENAME = 'input_small.txt'
#GRID_SIZE = 13
#FILENAME = 'input_small2.txt'

def make_grid()
  grid = Array.new(GRID_SIZE) { Array.new(GRID_SIZE) }
  ## Build init grid
  x = 1
  y = 1
  File.readlines(FILENAME).each do |line|
    x = 1
    line.chars.each do |char|
      grid[y][x] = char
      x += 1
    end
    y += 1
  end
  grid
end

def find_carts(grid)
  carts = []
  id = 1
  0.upto(GRID_SIZE - 1) do |y|
    0.upto(GRID_SIZE - 1) do |x|
      cart = nil
      if grid[y][x] == 'v'
        grid[y][x] = '|'
        cart = { x: x, y: y, dir: 'v', turn_num: 0, alive: true, id: id }
      elsif grid[y][x] == '^'
        grid[y][x] = '|'
        cart = { x: x, y: y, dir: '^', turn_num: 0, alive: true, id: id }
      elsif grid[y][x] == '>'
        grid[y][x] = '-'
        cart = { x: x, y: y, dir: '>', turn_num: 0, alive: true, id: id }
      elsif grid[y][x] == '<'
        grid[y][x] = '-'
        cart = { x: x, y: y, dir: '<', turn_num: 0, alive: true, id: id }
      end

      if cart != nil
        carts.push cart
        id += 1
      end
    end
  end

  [grid, carts]
end

def tick(grid, carts)
  carts = carts.sort_by { |x| x[:y] }
  carts.each_with_index do |cart|
    next if !cart[:alive]

    if cart[:dir] == 'v'
      cart[:y] += 1
    elsif cart[:dir] == '^'
      cart[:y] -= 1
    elsif cart[:dir] == '<'
      cart[:x] -= 1
    elsif cart[:dir] == '>'
      cart[:x] += 1
    end

    crash =
      carts.find do |c2|
        c2[:x] == cart[:x] && c2[:y] == cart[:y] && c2[:alive] &&
          c2[:id] != cart[:id]
      end
    if crash
      crash[:alive] = false
      cart[:alive] = false
      puts "Crash at #{cart[:x] - 1} #{cart[:y] - 1}"

      alive_carts = carts.select { |c| c[:alive] }
      if alive_carts.length == 1
        last_cart = alive_carts.first
        puts "One cart left at #{last_cart[:x] - 1} #{last_cart[:y] - 1}"
        pp last_cart
        puts 'You might have to move it once more to give it the answer it wants?'
        exit
      end
    end

    this_square = grid[cart[:y]][cart[:x]]
    if this_square == '+'
      if cart[:turn_num] == 0
        turn = 'left'
      elsif cart[:turn_num] == 1
        turn = 'straight'
      elsif cart[:turn_num] == 2
        turn = 'right'
      end

      cart[:dir] = do_turn(turn, cart[:dir])

      cart[:turn_num] += 1
      cart[:turn_num] = 0 if cart[:turn_num] == 3
    elsif this_square == '/'
      if cart[:dir] == '>'
        cart[:dir] = '^'
      elsif cart[:dir] == 'v'
        cart[:dir] = '<'
      elsif cart[:dir] == '^'
        cart[:dir] = '>'
      elsif cart[:dir] == '<'
        cart[:dir] = 'v'
      end
    elsif this_square == '\\'
      if cart[:dir] == '>'
        cart[:dir] = 'v'
      elsif cart[:dir] == 'v'
        cart[:dir] = '>'
      elsif cart[:dir] == '^'
        cart[:dir] = '<'
      elsif cart[:dir] == '<'
        cart[:dir] = '^'
      end
    end
  end
  carts
end

def do_turn(turn, direction)
  if turn == 'straight'
    return direction
  elsif turn == 'left'
    map = { '^' => '<', '<' => 'v', 'v' => '>', '>' => '^' }
    return map[direction]
  elsif turn == 'right'
    map = { '^' => '>', '<' => '^', 'v' => '<', '>' => 'v' }
    return map[direction]
  end
  direction
end

def print_map(grid, carts)
  0.upto(8) do |y|
    0.upto(GRID_SIZE - 1) do |x|
      candidates = carts.select { |c| c[:x] == x && c[:y] == y }
      if candidates.any?
        print candidates.first[:dir]
      else
        print grid[y][x]
      end
    end
    print "\n"
  end
  ''
end

def minus_one(carts)
  carts.map { |c| (c[:x] - 1).to_s + ',' + (c[:y] - 1).to_s }
end

def main
  grid = make_grid
  grid, carts = find_carts(grid)

  0.upto(100_015) do |i|
    carts = tick(grid, carts)
    #print_map(grid, carts)
    #pp '---'
    #pp minus_one(carts)
  end
end

# Guesses: (You guessed 57,47.)
# (You guessed 26,84.)

main