nushell

I'm still travelling, so another phone attempt. Jet lag says sleep, so just part 1 for now:

def part1 [filename: string] {
  mut input = open $filename | lines |
    each { parse '{index}: {children}' | update children { split row " " } | first } |
    insert paths { null }
  print $"Data loaded, ($input | length) devices"

  $input = explore-path $input you
  $input | where index == you | get 0.paths
}

def explore-path [devices, start: string] {
  print $"Exploring ($start)"
  let dev = $devices | where index == $start | first
  if ($dev | get paths) != null {
    print "Already explored"
    return $devices
  }

  # Shadow with mutable version
  mut devices = $devices
  mut paths = 0
  let is_out = $dev | get children | where ($it == out) | is-not-empty
  if $is_out {
    print $"Found an out device: ($start)"
    $paths = 1
  } else {
    for child in ($dev | get children ) {
      $devices = explore-path $devices $child
      $paths += $devices | where index == $child | get 0.paths
    }
  }

  # Shadow with immutable... wtf
  let paths = $paths
  print $"Setting paths for ($start) to ($paths)"
  $devices = $devices | update paths { |row| if $row.index == $start {  
$paths } else {} }
   $devices
}