Paste: AOC day 1 fast

USING: combinators deques dlists io.encodings.ascii io.files
kernel literals locals math math.parser prettyprint sequences
sorting ;
IN: aoc.2020.01fast

CONSTANT: input $[
    "resource:work/aoc/2020/01/input.txt" ascii file-lines
    [ string>number ] map natural-sort
]

DEFER: find-sum

:: (find-sum) ( deque target -- pair )
    deque peek-front :> low
    deque peek-back :> high
    low high + :> sum
    {
        { [ sum target = ] [ { low high } ] }
        { [ sum target < ] [ deque pop-front drop deque target find-sum ] }
        [ deque pop-back drop deque target find-sum ]
    } cond ;

: find-sum ( deque target -- pair/f )
    over deque-empty? [ 2drop f ] [ (find-sum) ] if ;

: >deq ( seq -- deque ) DL{ } clone [ push-all-back ] keep ;

: part1 ( -- ) input >deq 2020 find-sum product . ;

:: part2 ( -- )    ! Part 2 runs in about 2 ms.
    { } :> pair!
    input [ 2020 swap - input >deq swap find-sum dup pair! ]
    find nip pair first2 * * . ;