Advent of Code 2023 Day 10 Part 1

require 'pp'

input = File.readlines(ARGV[0] || 'example').map(&:rstrip)

start_row = start_col = 0
input.each_with_index do |line, row|
  if (col = line.index('S'))
    start_row = row
    start_col = col
    break
  end
end

puts "start at #{start_row}, #{start_col}"

width = input[0].length
height = input.length

# start by searching cardinal directions clockwise beacuse we don't
# know what shape pipe 'S' is
paths = []

# up
r, c = start_row-1, start_col
if r >= 0 && r < height && c >= 0 && c < width
  if '|7F'.index(input[r][c])
    paths << [r, c]
  end
end
# right
r, c = start_row, start_col+1
if r >= 0 && r < height && c >= 0 && c < width
  if '-J7'.index(input[r][c])
    paths << [r, c]
  end
end
# down
r, c = start_row+1, start_col
if r >= 0 && r < height && c >= 0 && c < width
  if '|LJ'.index(input[r][c])
    paths << [r, c]
  end
end
# left
r, c = start_row, start_col-1
if r >= 0 && r < height && c >= 0 && c < width
  if '-LF'.index(input[r][c])
    paths << [r, c]
  end
end

p paths

# clean up map
clean = [nil] * height
height.times { clean[_1] = '.' * width}

visited = {}

at = paths[0]
loop do
  #puts "at #{at.join(', ')}"
  visited[at] = true
  r, c = at
  clean[r][c] = input[r][c]
  candidates =
    case input[r][c]
    when '|' then [[r-1, c], [r+1, c]]
    when '-' then [[r, c-1], [r, c+1]]
    when 'L' then [[r-1, c], [r, c+1]]
    when 'J' then [[r-1, c], [r, c-1]]
    when '7' then [[r, c-1], [r+1, c]]
    when 'F' then [[r+1, c], [r, c+1]]
    when 'S' then break
    else
      next
    end
  #puts "candidates: #{candidates.inspect}"
  candidates.each do |pos|
    r, c = pos
    if r < 0 || r >= height || c < 0 || c >= width
      raise "#{at.join(', ')} -> #{r}, #{c} (out of bounds)"
    end
    if !visited[pos] # take this path
      #puts "taking [#{r}][#{c}] = #{input[r][c]}"
      at = pos
      break
    end
  end
  #puts "\nat #{at}"
  #pp clean
end

puts
clean.each {puts _1}

# now, follow both paths simultaneously until
counts = [nil] * height
height.times { counts[_1] = '.' * width}
counts[start_row][start_col] = '0'

visited = {[start_row, start_col] => true}
n = 1
max = 0
loop do
  puts "at #{paths[0].join(', ')} | #{paths[1].join(', ')}"
  nxt = paths.map do |at|
    visited[at] = true
    r, c = at
    counts[r][c] = (n % 10).to_s
    max = n if n > max
    candidates =
      case input[r][c]
      when '|' then [[r-1, c], [r+1, c]]
      when '-' then [[r, c-1], [r, c+1]]
      when 'L' then [[r-1, c], [r, c+1]]
      when 'J' then [[r-1, c], [r, c-1]]
      when '7' then [[r, c-1], [r+1, c]]
      when 'F' then [[r+1, c], [r, c+1]]
      when 'S' then [] # XXX at end! what do?
      else []
      end
    take = nil
    candidates.each do |pos|
      r, c = pos
      if r < 0 || r >= height || c < 0 || c >= width
        raise "#{at.join(', ')} -> #{r}, #{c} (out of bounds)"
      end
      if !visited[pos] # take this path
        puts "taking [#{r}][#{c}] = #{input[r][c]}"
        take = pos
        break
      end
    end
    if !take
      puts "no path to take! end?"
    end
    puts "at #{at} -> #{take}"
    take
  end
  print "nxt: "
  p nxt

  break if nxt.all?{_1 == nil}
  paths = nxt
  n += 1
end

puts
counts.each {puts _1}
puts
puts "max step = #{max}"