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34 lines
1000 B
Racket
34 lines
1000 B
Racket
#lang typed/racket
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(require typed/rackunit)
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(provide (all-defined-out))
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(define first-code 20151125)
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(: next-code (-> Integer Integer))
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(define (next-code code)
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(modulo (* code 252533) 33554393))
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(: nth-code (-> Integer Integer))
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(define (nth-code n)
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(for/fold : Integer ([code-so-far first-code])
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([i (in-range (sub1 n))])
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(next-code code-so-far)))
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(: rc->n (-> Integer Integer Integer))
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(define (rc->n row col)
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(define first-col-val (add1 (apply + (range row))))
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(define col-offset-val (apply + (range (add1 row) (+ row col))))
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(+ first-col-val col-offset-val))
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(: q1 (-> String Integer))
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(define (q1 input-str)
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(match-define (list _ row col)
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(map (λ ([s : (U #f String)]) (and s (string->number s)))
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(or (regexp-match #px"row (\\d+), column (\\d+)" input-str) (error 'bg))))
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(nth-code (rc->n (cast row Integer) (cast col Integer))))
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(module+ test
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(define input-str (file->string "../day25-input.txt"))
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(check-equal? (q1 input-str) 19980801))
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