day17

1 files changed, 63 insertions, 0 deletions

diff --git a/day17.lisp b/day17.lisp
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+(defun read-map (filespec)
+  (with-open-file (stream filespec)
+    (let ((lines (loop for line = (read-line stream nil)
+                       while line
+                       collect (make-array
+                                (length line)
+                                :initial-contents (loop for c across line
+                                                        collect (- (char-code c)
+                                                                   (char-code #\0)))))))
+      (make-array (list (length lines) (length (first lines))) :initial-contents lines))))
+
+(defun min-node (q)
+  (let ((mk ())
+        (mv -1))
+    (maphash (lambda (k v) (when (or (= mv -1) (< v mv)) (setf mk k mv v))) q)
+    mk))
+
+(defun best-path (map min-moves max-moves)
+  (let ((q (make-hash-table :test #'equalp))
+        (v (make-hash-table :test #'equalp))
+        (n (array-dimension map 0))
+        (m (array-dimension map 1)))
+    (labels ((is-final (node)
+               (multiple-value-bind (i j) (values-list node)
+                 (and (= i (1- n)) (= j (1- m)))))
+             (is-possible (node)
+               (multiple-value-bind (i j c) (values-list node)
+                 (and (>= i 0) (>= j 0) (< i n) (< j m) (<= c max-moves))))
+             (add-node (node val)
+               (unless (or (not (is-possible node)) (gethash node v))
+                 (multiple-value-bind (oval found-p) (gethash node q)
+                   (multiple-value-bind (i j) (values-list node)
+                     (let ((val (+ val (aref map i j))))
+                       (setf (gethash node q) (if found-p (min val oval) val))))))))
+      (setf (gethash '(0 1 1 #\R) q) (aref map 0 1))
+      (setf (gethash '(1 0 1 #\D) q) (aref map 1 0))
+      (loop for node = (min-node q)
+            while node
+            if (is-final node)
+              return (gethash node q)
+            do (multiple-value-bind (i j c d) (values-list node)
+                 (let ((val (gethash node q)))
+                   (remhash node q)
+                   (setf (gethash node v) val)
+                   (unless (or (equal d #\D) (and (not (equal d #\U)) (< c min-moves)))
+                     (add-node (list (1- i) j (if (equal d #\U) (1+ c) 1) #\U) val))
+                   (unless (or (equal d #\U) (and (not (equal d #\D)) (< c min-moves)))
+                     (add-node (list (1+ i) j (if (equal d #\D) (1+ c) 1) #\D) val))
+                   (unless (or (equal d #\R) (and (not (equal d #\L)) (< c min-moves)))
+                     (add-node (list i (1- j) (if (equal d #\L) (1+ c) 1) #\L) val))
+                   (unless (or (equal d #\L) (and (not (equal d #\R)) (< c min-moves)))
+                     (add-node (list i (1+ j) (if (equal d #\R) (1+ c) 1) #\R) val))))))))
+
+(defun solve1 (filespec)
+  (best-path (read-map filespec) 0 3))
+
+(defun solve2 (filespec)
+  (best-path (read-map filespec) 4 10))
+
+(print (solve1 "data/17/example.txt")) ;; 102
+(print (solve1 "data/17/input.txt"))   ;; 1039
+(print (solve2 "data/17/example.txt")) ;; 102
+(print (solve2 "data/17/input.txt"))   ;; 1201