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@@ -0,0 +1,70 @@
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+#lang racket
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+
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+(require "../lib/utils.rkt")
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+
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+(define lines
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+ (call-with-input-file "input"
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+ (λ (fp) (get-lines fp))))
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+
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+(set! lines (list->vector lines))
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+
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+(define (expand-rows lines)
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+ (let loop ((cur (vector->list lines)) (ret '()))
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+ (if (null? cur)
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+ (list->vector (reverse ret))
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+ (if (andmap (λ (c) (char=? c #\.)) (string->list (car cur)))
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+ (loop (cdr cur) (cons (car cur) (cons (car cur) ret)))
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+ (loop (cdr cur) (cons (car cur) ret))))))
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+
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+(define (transpose linesvec)
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+ (define lines (vector->list linesvec))
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+ (define width (string-length (vector-ref linesvec 0)))
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+ (define new-lines (make-vector width))
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+ (let loop ((i 0))
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+ (if (>= i width)
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+ new-lines
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+ (let ()
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+ (define char-list (map (λ (l) (string-ref l i)) lines))
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+ (vector-set! new-lines i (list->string char-list))
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+ (loop (+ i 1))))))
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+
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+(define universe
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+ (transpose (expand-rows (transpose (expand-rows lines)))))
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+
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+(define height (vector-length universe))
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+(define width (string-length (vector-ref universe 0)))
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+
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+(define (get-galaxies universe)
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+ (define (char-at x y) (string-ref (vector-ref universe y) x))
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+ (let loop ((x 0) (y 0) (ret '()))
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+ (if (>= y height)
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+ (list->vector (reverse ret))
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+ (if (>= x width)
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+ (loop 0 (+ y 1) ret)
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+ (if (char=? #\# (char-at x y))
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+ (loop (+ x 1) y (cons (cons x y) ret))
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+ (loop (+ x 1) y ret))))))
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+
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+(define galaxies (get-galaxies universe))
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+
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+(define (gen-pairs n)
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+ (let loop ((i 0) (j 1) (ret '()))
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+ (if (>= i n)
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+ (reverse ret)
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+ (if (>= j n)
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+ (loop (+ 1 i) (+ 2 i) ret)
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+ (loop i (+ 1 j) (cons (cons i j) ret))))))
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+
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+
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+
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+(define (distance n1 n2)
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+ (define x1 (car (vector-ref galaxies n1)))
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+ (define x2 (car (vector-ref galaxies n2)))
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+ (define y1 (cdr (vector-ref galaxies n1)))
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+ (define y2 (cdr (vector-ref galaxies n2)))
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+ (+ (abs (- x1 x2)) (abs (- y1 y2))))
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+
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+(apply
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+ +
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+ (map (λ (x) (distance (car x) (cdr x)))
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+ (gen-pairs (vector-length galaxies))))
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