23 lines
533 B
Racket
23 lines
533 B
Racket
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#lang racket
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(require "../lib.rkt")
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(define input (map string->number (problem-input 1)))
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(define part1
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(let loop ([entries input]
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[ht (hash)])
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(let ([entry (first entries)])
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(if (hash-has-key? ht entry)
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(* entry (hash-ref ht entry))
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(loop (rest entries) (hash-set ht (- 2020 entry) entry))))))
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(define part2
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(for*/first ([i input]
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[j (cdr input)]
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[k (cddr input)]
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#:when (= (+ i j k) 2020))
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(* i j k)))
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(show-solution part1 part2)
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