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47 lines
1.8 KiB
Racket
47 lines
1.8 KiB
Racket
#lang br/quicklang ;; http://adventofcode.com/2016/day/18
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(provide read-syntax
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cons
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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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#,@(for/list ([line (in-list (string-split (port->string port) "\n"))])
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`(cons ,@(map string->number (string-split line "-")))))))
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(define-macro (mb . RANGE-PAIRS)
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#'(#%module-begin
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(define range-pairs (sort (list . RANGE-PAIRS) < #:key car))
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(solve-a range-pairs)
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(solve-b range-pairs)))
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(define (solve-a range-pairs)
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(for/first ([left (in-list range-pairs)]
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[right (in-list (cdr range-pairs))]
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#:when (> (- (car right) (cdr left)) 1))
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(add1 (cdr left))))
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(define (find-overlap n ranges)
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(and (pair? ranges)
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(for/first ([r (in-list ranges)]
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#:when (<= (car r) n (cdr r)))
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r)))
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(define (solve-b range-pairs)
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(define rps (for/fold ([rps empty])
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([rp (in-list (append range-pairs '((4294967295 . 4294967295))))])
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(define next-rps rps)
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(define left (or
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(let ([result (find-overlap (car rp) rps)])
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(and result (set! next-rps (remove result next-rps)) (car result)))
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(car rp)))
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(define right (or
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(let ([result (find-overlap (cdr rp) rps)])
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(and result (set! next-rps (remove result next-rps)) (cdr result)))
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(cdr rp)))
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(cons (cons left right) next-rps)))
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(define sorted-rps (sort rps < #:key car))
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(for/sum ([left (in-list sorted-rps)]
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[right (in-list (cdr sorted-rps))]
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#:when (> (- (car right) (cdr left)) 1))
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(- (car right) (cdr left) 1))) |