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43 lines
1.4 KiB
Racket
43 lines
1.4 KiB
Racket
4 years ago
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#lang br
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(require racket/file rackunit)
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(define grid
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(for*/hasheqv ([(row ridx) (in-indexed (file->lines "11.rktd"))]
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[(col cidx) (in-indexed row)])
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(values (make-rectangular cidx ridx) col)))
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(define (seat-count grid)
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(count (λ (val) (char=? val #\#)) (hash-values grid)))
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(define offsets '(-1-1i -1 -1+i +i 1+i 1 1-i -i))
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(define (visible-occupied-seats grid k [adjacent-only? #false])
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(for/sum ([offset (in-list offsets)])
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(let loop ([k (+ k offset)] [sum 0])
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(match (hash-ref grid k #false)
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[#false sum]
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[#\# 1]
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[#\L 0]
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[_ (if adjacent-only?
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sum
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(loop (+ k offset) sum))]))))
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(define (adjacent-occupied-seats grid k) (visible-occupied-seats grid k #true))
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(define (iterate grid seat-counter threshold)
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(for/hasheqv ([(k v) (in-hash grid)])
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(match v
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[#\L #:when (zero? (seat-counter grid k)) (values k #\#)]
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[#\# #:when (<= threshold (seat-counter grid k)) (values k #\L)]
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[_ (values k v)])))
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(define (solve grid iteration-proc)
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(let loop ([grid grid])
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(define next-grid (iteration-proc grid))
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(if (eqv? (seat-count grid) (seat-count next-grid))
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(seat-count grid)
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(solve next-grid iteration-proc))))
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(check-equal? (solve grid (λ (grid) (iterate grid adjacent-occupied-seats 4))) 2489)
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(check-equal? (solve grid (λ (grid) (iterate grid visible-occupied-seats 5))) 2180)
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