From eb382643923041b00a032ae71cac8b40dc716698 Mon Sep 17 00:00:00 2001
From: Oscar Najera <hi@oscarnajera.com>
Date: Tue, 13 Dec 2022 02:52:09 +0100
Subject: lisp read

---
 AoC2022/12/solver.lisp | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

(limited to 'AoC2022/12/solver.lisp')

diff --git a/AoC2022/12/solver.lisp b/AoC2022/12/solver.lisp
index b2a0752..e0320c3 100644
--- a/AoC2022/12/solver.lisp
+++ b/AoC2022/12/solver.lisp
@@ -17,28 +17,28 @@
                (when (<  0 y height) (- pos width)))     ;; up move
               :test #'eq))))
 
-(defun elevations (data)
-  (map 'vector (lambda (chr)
-                    (case chr
-                      (#\S 0)
-                      (#\E 27)
-                      (t (- (char-code chr) 96))))
-       data))
+(defun elevation (chr)
+  (case chr
+    (#\S 0)
+    (#\E 27)
+    (t (- (char-code chr) 96))))
 
 (defun land (input-file)
   (let ((data (uiop:read-file-lines input-file)))
-    (make-land :elevation (elevations (apply #'concatenate 'string data))
+    (make-land :elevation (map 'vector #'elevation (apply #'concatenate 'string data))
                :neighbors (possible-directions (length (car data)) (length data)))))
 
+(defun appropriate (place elevation land paths)
+  (and (not (gethash place paths)) ;; not visited
+       (>= elevation (aref (land-elevation land) place))))
+
 (defun next-steps (place land paths)
   (let ((elevation (aref (land-elevation land) place)))
     (unless (= 27 elevation)
-      (mapcan (lambda (option)
-                (when (and (not (gethash option paths))
-                           (>= (1+ elevation) (aref (land-elevation land) option)))
-                  (setf (gethash option paths) (cons option (gethash place paths)))
-                  (list option)))
-              (funcall (land-neighbors land) place)))))
+      (loop :for option :in (funcall (land-neighbors land) place)
+            :when (appropriate option (1+ elevation) land paths)
+              :do (setf (gethash option paths) (cons option (gethash place paths)))
+              :and collect option))))
 
 (defun shortest-path (starts land paths)
   (let ((next (mapcan (lambda (place) (next-steps place land paths)) starts)))
@@ -51,7 +51,9 @@
          (finish (position 27 (land-elevation land) :test #'eq))
          (starts (loop for i from 0
                        for el across (land-elevation land)
-                       when (funcall start-p el) collect (progn (setf (gethash i paths) (list i)) i))))
+                       when (funcall start-p el)
+                         do (setf (gethash i paths) (list i))
+                         and collect i)))
     (shortest-path starts land paths)
     (1- (length (gethash finish paths)))))
 
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