81 lines
2.6 KiB
Racket
81 lines
2.6 KiB
Racket
#lang racket
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(module+ test
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(require rackunit))
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(module+ main
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(displayln "Day 14"))
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(define (read-rules filename)
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(with-input-from-file filename
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(lambda ()
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(define h (make-hash))
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(for ([line (in-lines)])
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(define rule
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(for/list ([elt (regexp-match* #rx"([0-9]+) ([A-Z]+)" line #:match-select cdr)])
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(list (string->number (car elt)) (string->symbol (cadr elt)))))
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(define output (last rule))
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(hash-set! h
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(cadr output)
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(cons (car output)
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(make-hash (for/list ([elt (drop-right rule 1)])
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(cons (cadr elt) (car elt)))))))
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h)))
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(define (generate! rules needed available)
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(for ([(target target-amount) (in-hash needed)]
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#:unless (eq? target 'ORE))
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(define inputs (cdr (hash-ref rules target)))
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(define output-amount (car (hash-ref rules target)))
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(define new-target-amount (- target-amount (hash-ref available target 0)))
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(define multiple (ceiling (/ new-target-amount output-amount)))
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(hash-set! available target (- (* multiple output-amount) new-target-amount))
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(hash-set! needed target 0)
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(for ([(input input-amount) (in-hash inputs)])
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(hash-update! needed input (lambda (v) (+ v (* multiple input-amount))) 0))))
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(define (ore-per-fuel rules amount)
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(define needed (make-hash `((FUEL . ,amount))))
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(define available (make-hash))
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(for ([i (in-naturals)]
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#:break (= (apply + (hash-values needed)) (hash-ref needed 'ORE 0)))
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(generate! rules needed available))
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(hash-ref needed 'ORE))
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(define (part1 filename)
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(define rules (read-rules filename))
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(ore-per-fuel rules 1))
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(module+ test
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(check-eq? 31 (part1 "test1"))
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(check-eq? 165 (part1 "test2"))
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(check-eq? 13312 (part1 "test3"))
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(check-eq? 180697 (part1 "test4"))
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(check-eq? 2210736 (part1 "test5")))
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(module+ main
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(display "Part 1: ")
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(displayln (part1 "input")))
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(define (part2 filename)
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(define rules (read-rules filename))
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(define max-fuel 1000000000000)
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(define min-fuel 1)
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(bisect rules 1000000000000 min-fuel max-fuel))
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(define (bisect rules target-ore min-fuel max-fuel)
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(define mid-fuel (floor (+ min-fuel (/ (- max-fuel min-fuel) 2))))
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(define ore (ore-per-fuel rules mid-fuel))
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(cond
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[(= 1 (- max-fuel min-fuel)) min-fuel]
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[(< ore target-ore) (bisect rules target-ore mid-fuel max-fuel)]
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[(< target-ore ore) (bisect rules target-ore min-fuel mid-fuel)]))
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(module+ test
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(check-eq? 82892753 (part2 "test3"))
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(check-eq? 5586022 (part2 "test4"))
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(check-eq? 460664 (part2 "test5")))
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(module+ main
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(display "Part 2: ")
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(displayln (part2 "input")))
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