Day 18: Partial progress.

input/18.txt

@@ -0,0 +1,81 @@
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lib.rkt

@@ -11,6 +11,7 @@
          show-solution
 
          make-vector-grid
+         lists->vectors
          vectors->lists
          hash->vectors
          show-list-grid
@@ -78,6 +79,10 @@
 (define (make-vector-grid width height [default 0])
   (build-vector height (λ (_) (make-vector width default))))
 
+;; lists->vectors : list-grid -> vector-grid
+(define (lists->vectors list-grid)
+  (list->vector (map list->vector list-grid)))
+
 ;; vectors->lists : vector-grid -> list-grid
 (define (vectors->lists vector-grid)
   (map vector->list (vector->list vector-grid)))
@@ -118,6 +123,13 @@
   (show-vector-grid char-hash (hash->vectors hash-grid default)))
 
 
+;; Char helpers ;;
+
+;; nchar=? : char -> char -> boolean
+(define (nchar=? c1 c2)
+  (not (char=? c1 c2)))
+
+
 ;; Number helpers ;;
 
 ;; sum : (listof number) -> number
@@ -127,10 +139,6 @@
 (define (!= n1 n2)
   (not (= n1 n2)))
 
-;; nchar=? : char -> char -> boolean
-(define (nchar=? c1 c2)
-  (not (char=? c1 c2)))
-
 ;; nzero? : number -> boolean
 (define (nzero? n)
   (not (zero? n)))

src/18.rkt

@@ -0,0 +1,74 @@
+#lang racket
+
+(require data/queue
+         graph
+         (except-in "../lib.rkt" transpose))
+
+(define input
+  (problem-input 18))
+
+(define list-grid
+  (map string->list input))
+
+(define vector-grid
+  (lists->vectors list-grid))
+
+(define width
+  (length (car list-grid)))
+
+(define height
+  (length list-grid))
+  
+(define (get-char coord)
+  (match-let ([(list x y) coord])
+    (if (or (< x 0) (< y 0)
+            (>= x width)
+            (>= y height))
+        #\#
+        (vector-ref (vector-ref vector-grid y) x))))
+
+(define (neighbours coord)
+  (match-let ([(list x y) coord])
+    (let ([U (list x (sub1 y))]
+          [D (list x (add1 y))]
+          [L (list (sub1 x) y)]
+          [R (list (add1 x) y)])
+      (filter-not
+       (∘ (∂ char=? #\#) (∂ get-char))
+       (list U D L R)))))
+
+(define key-door-graph
+  (let* ([Q (make-queue)]
+         [entrance (list (round (/ width 2))
+                         (round (/ height 2)))]
+         [visited (make-hash `((,entrance . #t)))]
+         [graph (weighted-graph/undirected '())])
+    (enqueue! Q (list entrance #\@ 0))
+    (let loop ()
+      (if (queue-empty? Q)
+          graph
+          (match-let* ([(list coord prev dist) (dequeue! Q)]
+                       [ncoords (neighbours coord)])
+            (for-each
+             (λ (ncoord)
+               (let ([nc (get-char ncoord)])
+                 (cond
+                   [(hash-ref visited ncoord #f)]
+                   [(char=? #\. nc)
+                    (hash-set! visited ncoord #t)
+                    (enqueue! Q (list ncoord prev (add1 dist)))]
+                   [else
+                    (hash-set! visited ncoord #t)
+                    (enqueue! Q (list ncoord nc 0))
+                    (add-edge! graph prev nc (add1 dist))])))
+             ncoords)
+            (loop))))))
+
+(define ordered-keys
+  (let ([keys (filter char-lower-case? (get-vertices key-door-graph))])
+    (displayln keys)
+    (define (sort-fn c1 c2)
+      (not (member (char-upcase c2) (fewest-vertices-path key-door-graph #\@ c1))))
+    (sort keys sort-fn)))
+
+#;(for-each displayln (map (λ (s) (string-replace (string-replace s "#" "█") "." " ")) input))