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31 lines
997 B
Racket
31 lines
997 B
Racket
8 years ago
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#lang br/quicklang ;; http://adventofcode.com/2016/day/18
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(provide read-syntax
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(rename-out [mb #%module-begin]))
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(define (read-syntax path port)
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(strip-bindings
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#`(module mod "lang.rkt"
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#,(string-trim (port->string port)))))
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(define-macro (mb STR)
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#'(#%module-begin
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(define (traps cs)
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(length (filter (λ(c) (char=? #\. c)) cs)))
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(let loop ([cs (string->list STR)]
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[count (traps (string->list STR))]
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[i 0])
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(if (= i 399999) ; number of rows
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count
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(let* ([result (next-cs cs)]
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[this-count (traps result)])
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(loop result (+ this-count count) (add1 i)))))))
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(define (next-cs cs)
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(define adj-cs (append (list #\.) cs (list #\.)))
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(for/list ([c1 (in-list adj-cs)]
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[c2 (in-list (cdr adj-cs))]
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[c3 (in-list (cddr adj-cs))])
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(case (list c1 c2 c3)
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[((#\^ #\^ #\.) (#\. #\^ #\^) (#\^ #\. #\.) (#\. #\. #\^)) #\^]
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[else #\.])))
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