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36 lines
1.6 KiB
Racket
36 lines
1.6 KiB
Racket
#lang typed/racket
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(require typed/rackunit (only-in math divisors))
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(provide (all-defined-out))
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(: q1 (-> String (U #f Integer)))
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(define (q1 input-str)
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(define target-gifts (cast (read (open-input-string input-str)) Natural))
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(define gifts-per-elf 10)
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(for/or : (U #f Integer) ([house-number (in-naturals)]
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#:when (let* ([elves (divisors house-number)]
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[elf-gifts
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(apply + (map (ann (curry * gifts-per-elf) (-> Natural Natural)) elves))])
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(>= elf-gifts target-gifts)))
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house-number))
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(: q2 (-> String (U #f Integer)))
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(define (q2 input-str)
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(define target-gifts (cast (read (open-input-string input-str)) Natural))
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(define gifts-per-elf 11)
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(for/or : (U #f Integer) ([house-number (in-naturals)]
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#:when (let* ([elves (divisors house-number)]
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[elves (filter
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(λ([e : Integer]) (<= house-number (* 50 e))) elves)]
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[elf-gifts
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(apply + (map (ann (curry * gifts-per-elf) (-> Natural Natural)) elves))])
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(>= elf-gifts target-gifts)))
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house-number))
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(module+ test
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(define input-str (file->string "../day20-input.txt"))
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(check-equal? (q1 input-str) 831600)
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(check-equal? (q2 input-str) 884520))
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