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#lang racket
(require "../../jj-aoc.rkt"
threading)
(define entries
(~>> (open-day 01 2020)
(port->list read)
list->set))
;; part 1
(define (look-for-complement xs)
(define x (set-first xs))
(cond
[(set-member? xs (- 2020 x)) (* x (- 2020 x))]
[else (look-for-complement (set-rest xs))]))
(time (look-for-complement entries))
;; part 2
(time (for*/first ([x (in-set entries)]
[y (in-set (set-subtract entries (set x)))]
#:when (set-member? (set-subtract entries (set x y)) (- 2020 x y)))
(* x y (- 2020 x y))))
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