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#lang racket
(require advent-of-code
threading
math/statistics)
(define crab-data
(~> (open-aoc-input (find-session) 2021 7 #:cache #t)
port->string
string-trim
(string-split ",")
(map string->number _)))
(define (gauss-sum n)
(/ (* n (+ n 1)) 2))
(define (compute-fuel-use f crabs align-to)
(for/sum ([crab (in-list crabs)]) (f (abs (- crab align-to)))))
;; using the fact that the optimum location is at the median
;; of the crabs' starting location for the linear relationship
;; and at a coordinate within 1 unit of the mean for the quadratic one
(~>> crab-data (median <) (compute-fuel-use identity crab-data))
(~>> crab-data
mean
((λ (m) (list (floor m) (ceiling m))))
(map (curry compute-fuel-use gauss-sum crab-data))
(apply min))
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