day24

2 files changed, 98 insertions, 0 deletions

diff --git a/day24 b/day24
new file mode 100644
index 0000000..f64ff83
--- /dev/null
+++ b/day24
@@ -0,0 +1,22 @@
+#.######################################################################################################################################################
+#<v^>^>^^<><^>^^v>vv^v^>>^<>^<v<>v^>>v>v><^..><v<^v<<^v>v>>>>^<v^>>>.v>.v><<v><.^>>^^^>v>>^.<v>>vv<<.<<v<<vv^<^>^v>^v<>^^.^.<<<v^>>^<^>.>vvv><^<^>v.^<>#
+#<..v<<^^.^^v<<>>v<vv.><v<<<>>>.<>>^vv^^v>v^>><v<.<<v.v^^>>v^vv<<><>>v.>.v>.<..v>^^>^<<vv>><>vv>>v>.><.<<vv<v^..v<v<v^v>v^vv<v<v^.^<v<.<<><>vvvvv^<^v>.#
+#<>>^<v>v^v>v>.^v<>v<v^<<<.^^<.>vv>>^<<^>>v<v.>^^^.<<<.>>v.>.v^<v><v>.>>>^><>v>>v^<.v^<.vv^>^v<><>>v^^<^>..<v><<^<<<^<v><^>^<>v>vvv>>^<<>><><<^^.<<v>v>#
+#>.<<<^..>><>v>^vv>vv<v..^>^^>>.><^<v.>>><^.^<>^v>.<^<>>>^>>^><^><^.^>.><><><^>^>>^>>>^<.>>^<^>vv<^v^><vv^v>.>^>>vv.^<>>^>>>><>.^.>v<.^<>v^>v>^^>>v<><>#
+#>>v<^v^<^^><>><>.>v^v>^v.>v^.>>.><><<>^><<>^>^v>v^^^>>^v<<<>v<vv>v>>v<^^^<<<<v^vv><>v<^>>.<v.^^>^v<v<v.v..v<^^>>><.v^<.>>vv>v><><.^^^v><.<<v^>^>>><v><#
+#>>vv<^vv<<v<^v^.><>^<v<>v<^v.>>v<><>.>^.^....<<^<.<v>><v>^^^<><>.>^<<v^<>>>^^><v><>>v^v<v<v^<.^<v>v^<>v^<vv^.<^v>^^^v.<><^><^v<<.v>>><>>><.v>v>>^.^>^>#
+#<v<>>^v>v^vv^.^<<<^><>v^<.>>^^^<^<^>.>>^<<.^>><<<v^v>.>^^.vv>.v<v^>v><^^.<<<v^>v..<^<.vvv<.<v..<.>.v>.>>^v<^^<^v^>^.<<^^.^^<><v^^v<^^^v>v<<<<v<<>v>><>#
+#<^>>^>><<>v.v>.vvv><^><v<^v<>v..<<<>>><<vv>^v><^>..<^^v>.<<<v><v^^vv^^>>.v..^<.^v<v>v.><vv>^><>vv><<>v^>v>><^^>^>><^>.>^^<<><><^.>^v<>v^.>v><>>.v^..v>#
+#<.<<<^><><^<<^>><..>^<<<>^.<>>v..v^^<<<.><.^.<^>^vvv^^^^>v>^<v>>>>>v<><>v.<>>^.<>v^<.^vv>v^<v>.><v<^.><<^vv<>><>v><^v>>^^^.v^v>v>^v^>.v<<^>.^v<v>^>vv<#
+#<<>^^.^>v<vvvv<<^v<v<<<v>.<>>^>^.<<^>^><<>v^.><<<.^^^<<^><<^^>.>vv<v<>>^>^^v<.^>.<v<>^>^<^>^.<>^v.^^^.v><v>^.^v^<<<><<>v.>>>>^<v>..v>^^v<v<^>v<v.>^v>>#
+#<^.<^^><>^^^<<>>^>.^^^<^<^<^^<^v.^^v>^v<>.^v^^<<..v<^<>>^<..<^.>><v<>^>.^v.>>v^.v..v.<<vv^>^vvv^v<vv<^.^><><><<^v^v.^^<<>^vv>^^>v>^v<<^>^<vvv.><^.^<v>#
+#<^^v^v>^<^><>v><.><v>^>^<vv<>..v^>^v^>^><>v<^v^<<v<<<<v<v..^^^<><v>v>^vv<^v.<><>vv>>>>v<>^vv<^v<>^^.v>>^^<<.<^<v<>>^>>vv>vv^<v^^>>^<v<.v<v>v<<>.>^>^v>#
+#<<>>>.<<>^>>v>^<^v>><<^v<><<.^<^<>>><^v>>v>^<^vv.<^^^.vv^<<<>^^>v>^v.>^^v>v.<>vvv><<v>v>^v.<v^<>^>vv<><vv<v^<><vv.>^>.>.v^v.v^vv^<.<>.>vv>^>v<v<v>^<.<#
+#>^<^<v<^^<^^v><<.<<..>>.>^^v>>v>^^>^^>>>v>v^<v^><>v>><v^<v>^>vvv>><>>vv>.>^.^<>.><v.>^.v<><v<^v><v.v<v<..^>^^<^v^>>.>v.v<><<<v><>^<<^>^>^>^.vv..<>v<^>#
+#..v<<^v^^>^>^<^<vvv>v<v^^v^.<<vvv.v.v^v>^v^^v>><^><<^v.<vv<><.vv^v<<>^v<<^v^v^^.>^>v<^^v...>>vv.<^v>v^<<^<vv>v^>v<^>v<vv>^<>.>v^^^^.^<>^^.^><.<.>>.><.#
+#<vv>v^<v^.vv<<.>v<<^v^>>^vv.v>>v>.vv^>>vv.>v>>>^.>>><.^.^<><>^vv<^<>><<vv<<v>^v^>>.<v^<v^<^^^<><>v<>v<....^^><.<^^>v^v>v<v<.><<>>^<>.v.<.vv<.>^.^v^>.>#
+#<<v<^vv^>v>>^>.>^^^<.>>^<><>>.>^v^<.v^^.^<<^>^.^v^^v<v<><>>.>.<>.^.v>.<v>^><^>v>v<>.^v<><.<<.><<^v<><><^>v^...v<<^^<^>v>^^vv^^vvv>^>v>>.>>v^^.vv>^<v<>#
+#>v<>^v><>^>>><<^.^v<<v^>v<>>>.^v><^v<<>v<^^.<.><><v>^<><.v<v<<^^^>>><^>^>>.<>vvvv.^^v<<>^<>>><<v^v><v>>>^v.<^>.^>><v><<><vv.v<vv<v^^>v<.<^<^>v^^>v^.><#
+#><v>vv^<^.<^>v^v^<><><vvv^v>v<>>v^<>^>>>^v^<v>>v<<^.^<v^vvv^^<><vvv.<vv^.>>v^<v.^vv><vv<>v^<^<^^>^^^vv^.<><>><^v.<^<.<>.>^<^<^<>v<^.<v<v<v>^vv><.v<^>>#
+#>v^.v>^v<>>v^>>>^^^^>.v<<^>^v>.^^>^>v^<^v^^<^^v>v>.v^<v>^v><^^.><^^>>v>v^v<v.<^>><>vv><v^v^><>^vvv>>v>>^v^^<^>>v^<^vv^<^^^^vv<><vv<.v^><v>^^>v^v<><<<<#
+######################################################################################################################################################.#
diff --git a/day24.rkt b/day24.rkt
new file mode 100644
index 0000000..6b56406
--- /dev/null
+++ b/day24.rkt
@@ -0,0 +1,76 @@
+#lang racket
+
+(require data/heap)
+
+(define field
+  (for/list ([line (file->lines "day24")])
+    (for/list ([char line])
+      char)))
+
+(define width (length (first field)))
+(define height (length field))
+
+(define period (lcm (- width 2) (- height 2)))
+
+(define pos (mutable-set))
+
+(for ([(line y) (in-indexed field)])
+  (for ([(c x) (in-indexed line)])
+    (match c
+      [#\# (for ([z (in-range 0 period)])
+             (set-add! pos (vector x y z)))]
+      [#\< (for ([z (in-range 0 period)])
+             (set-add! pos (vector (+ 1 (modulo (- x 1 z) (- width 2))) y z)))]
+      [#\> (for ([z (in-range 0 period)])
+             (set-add! pos (vector (+ 1 (modulo (- x 1 (- z)) (- width 2))) y z)))]
+
+      [#\^ (for ([z (in-range 0 period)])
+             (set-add! pos (vector x (+ 1 (modulo (- y 1 z) (- height 2))) z)))]
+      [#\v (for ([z (in-range 0 period)])
+             (set-add! pos (vector x (+ 1 (modulo (- y 1 (- z)) (- height 2))) z)))]
+      [#\. (void)])))
+
+(define source (index-of (first field) #\.))
+(define target (index-of (last field) #\.))
+
+;; close behind source and target
+(for ([z (in-range 0 period)])
+  (set-add! pos (vector source -1 z))
+  (set-add! pos (vector target (length field) z)))
+
+(define (first<=? a b)
+  (<= (first a) (first b)))
+
+(define (distance pos source target period)
+  (define distances (make-hash))
+  (define queue (make-heap first<=?))
+
+  (hash-set! distances source 0)
+  (heap-add! queue (list 0 source))
+
+  (let loop ()
+    (if (zero? (heap-count queue))
+      #f
+      (let ([item (heap-min queue)])
+        (heap-remove-min! queue)
+        (if (equal? (vector-take (second item) 2) target)
+          (first item)
+          (let ([ndist (+ 1 (first item))]
+                [z (modulo (+ (vector-ref (second item) 2) 1) period)])
+            (for ([x (list -1 1  0 0 0)]
+                  [y (list  0 0 -1 1 0)])
+              (let ([neighbor (vector (+ x (vector-ref (second item) 0))
+                                      (+ y (vector-ref (second item) 1))
+                                      z)])
+                (unless (set-member? pos neighbor)
+                  (let [(dist (hash-ref distances neighbor 999999))]
+                    (when (> dist ndist)
+                      (hash-set! distances neighbor ndist)
+                      (heap-add! queue (list ndist neighbor)))))))
+            (loop)))))))
+
+(let* ([a (distance pos (vector source 0 0) (vector target (- height 1)) period)]
+       [b (distance pos (vector target (- height 1) a) (vector source 0) period)]
+       [c (distance pos (vector source 0 (+ a b)) (vector target (- height 1)) period)])
+  (values a                             ;; 332
+          (+ a b c)))                   ;; 942