Daily Programmer #206

dp206.rkt

#lang racket

(define width 91)
(define height 51)
(define radius 9)
(define test-input #<<GRID
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GRID
)           

(define test-grid (map string->list (string-split test-input "\n")))

(define (get-circle-points w h cx cy r)
  (for*/list ([x (stream-map (λ (i) (+ cx i)) 
                             (in-range (- r) (add1 r)))]
              [y (stream-map (λ (i) (+ cy i)) 
                             (in-range (- r) (add1 r)))]
              #:unless (or
                        (> 0 x)(> 0 y)
                        (<= w x) (<= h y)
                        (< r (sqrt (+ (expt (- cx x) 2)
                                      (expt (- cy y) 2))))))
    (list x y)))

(define (lookup grid point)
  (match-define (list x y) point)
  (list-ref (list-ref grid y) x))

(define (count-wartered-crops grid w h cx cy r)
  (define points (get-circle-points w h cx cy r))
  (for/fold ([n 0])
            ([p points]
             #:unless (eq? p (list cx cy)))
    (if (char=? (lookup grid p) #\x)
        (add1 n) 
        n)))

(define (find-max-point grid w h r)
  (define (loop cx cy max max-point)
    (if (and (= (- w 1) cx)
             (= (- h 1) cy))
        (values max max-point)
        (begin 
          (let*  
              ([wartered-at-point 
                (count-wartered-crops grid w h cx cy r)]
               [new-x (modulo (+ cx 1) w)]
               [new-y (if (zero? new-x) (+ cy 1) cy)])
            (if (< max wartered-at-point)
                (loop new-x new-y wartered-at-point (list cx cy))
                (loop new-x new-y max max-point))))))
  (loop 0 0 -1 #f))

(define (display-wartered-grid grid w h r max-point)
  (define wartered-points (get-circle-points w h (first max-point) (second max-point) r))
  (for* ([x (range h)]
         [y (range w)])
    (let ([char-at-point (lookup grid (list y x))])
      (if (and 
           (member (list x y) wartered-points)
           (char=? #\. char-at-point))
          (display "~")
          (display char-at-point)))
    (when (= y (- w 1)) (newline))))

(define (dailyprogrammer-206)
  (define-values [max max-point] 
    (find-max-point test-grid width height radius))
  (displayln (format "Max point is (~a, ~a) with ~a wartered." 
                     (first max-point) 
                     (second max-point)
                     max))
  (display-wartered-grid test-grid width height radius max-point))

Output:

> (dailyprogrammer-206)
Max point is (11, 10) with 35 wartered.
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>