a10.tt

composer toInt
  <INT>
end toInt

templates mergesort
  templates merge
    @: $(2);
    [ $(1)... -> \(
      when <?($@merge<[](0)>)
      | ..$@merge(1)> do
        $ !
      otherwise
        ^@merge(1) !
        $ -> #
     \),
     $@...] !
  end merge
  $ -> #

  when <[](0..1)> do $!
  otherwise
    def half: $::length ~/ 2;
    [$(1..$half) -> mergesort, $($half+1..last) -> mergesort] -> merge !
end mergesort

def adapters: [$IN::lines -> toInt] -> mergesort;

source part1
  @:[1..3 -> 0];
  @($adapters(1)): 1;
  @(3): $@(3) + 1;
  2..$adapters::length -> $adapters($) - $adapters($-1) -> @($): $@($) + 1;
  $@(1) * $@(3) !
end part1

'$part1;
' -> !OUT::write

source part2
  @: [1, 1, 1, 4..$adapters(last)+3 -> 0];
  $adapters... -> #
  $@(last) !
  <> def adapter: $;
    1..3 -> @($adapter+$): $@($adapter+$) + $@($adapter);
end part2

'$part2;
' -> !OUT::write