-
Notifications
You must be signed in to change notification settings - Fork 0
/
day13.lisp
111 lines (98 loc) · 4.27 KB
/
day13.lisp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
;;;; day13.lisp
(in-package :advent-of-code-2018)
;;;minecart = (list row-major-pos direction turn-count)
(defstruct minecart
pos
direction
(turns 0)
(crashed nil))
(defun day13-minecart-p (char)
(find char "<>^v"))
(defun day13-horizontal-p (char)
(find char "<>"))
(defun day13-parse-input (&optional (input (read-puzzlefile "input13.txt")))
(let* ((board (make-array (list (length input)
(length (first input)))
:initial-contents input))
(minecarts (loop
:for index :below (array-total-size board)
:for sign := (row-major-aref board index)
:when (day13-minecart-p sign)
:collect (make-minecart :pos index :direction sign)
:and :do (setf (row-major-aref board index)
(if (day13-horizontal-p sign)
#\-
#\|)))))
(list board minecarts)))
(defun day13-turn (minecart)
(setf (minecart-direction minecart)
(char "<^>v<^>v<^>v" (+ 3
(mod (minecart-turns minecart) 3)
(position (minecart-direction minecart) "<^>v"))))
(incf (minecart-turns minecart)))
(defun day13-move-cart! (board cart)
(with-accessors ((pos minecart-pos) (direction minecart-direction) (turns minecart-turns)) cart
(let* ((width (array-dimension board 1)))
(incf pos (case direction
(#\> 1)
(#\< -1)
(#\^ (- width))
(#\v width)
(t (error "This ain't no minecart's direction: ~a~%" direction))))
(case (row-major-aref board pos)
((#\- #\|) t)
(#\\ (setf direction (case direction
(#\> #\v)
(#\v #\>)
(#\< #\^)
(#\^ #\<))))
(#\/ (setf direction (case direction
(#\> #\^)
(#\v #\<)
(#\< #\v)
(#\^ #\>))))
(#\+ (day13-turn cart)))
cart)))
(defun day13-check-collision! (cart minecarts)
(let ((collisions
(remove-if #'minecart-crashed
(remove (minecart-pos cart) minecarts :key #'minecart-pos :test (complement #'=)))))
(unless (= 1 (length collisions))
(mapc (lambda (c) (setf (minecart-crashed c) t)) collisions))))
(defun day13-step! (board minecarts)
(loop
:for minecart :in (sort (copy-list minecarts) #'< :key #'minecart-pos)
:unless (minecart-crashed minecart)
:do (day13-move-cart! board minecart)
:and :do (day13-check-collision! minecart minecarts)))
(defun day13-pos->coord (board pos)
(multiple-value-bind (y x) (floor pos (array-dimension board 1))
(list x y)))
(defun day13 ()
(destructuring-bind (board carts) (day13-parse-input)
(loop
:until (some #'minecart-crashed carts)
:do (day13-step! board carts)
:finally
(format t "The first crash occurs at (~{~a~^,~}).~%"
(day13-pos->coord board (minecart-pos (find-if #'minecart-crashed carts)))))
(loop
:for uncrashed := (remove-if #'minecart-crashed carts)
:until (= 1 (length uncrashed))
:do (day13-step! board uncrashed)
:finally
(format t "After the last crash the last minecart is at (~{~a~^,~}).~%"
(day13-pos->coord board (minecart-pos (first uncrashed)))))))
;;helper - bit ugly
(defun day13-print-state (board minecarts)
(let* ((width (array-dimension board 1))
(copy (make-array (array-dimensions board)
:displaced-to (copy-seq
(make-array (array-total-size board) :displaced-to board)))))
(loop :for cart :in minecarts
:do (setf (row-major-aref copy (minecart-pos cart)) (minecart-direction cart))
:finally
(format t "~{~a~%~}~%"
(loop :for y :below (array-dimension board 0)
:collect (coerce (make-array width :displaced-to copy :displaced-index-offset (* y width))
'string))))))