adventofcode2022

commit 6e001c3958573cf0405b0dcce36562249128a024
parent a2d0a6eff5d84df8ef90e97f21847edf03dd8fcf
Author: Lukas Henkel <lh@entf.net>
Date:   Fri,  9 Dec 2022 13:35:09 +0100

Day 9 task 2

Diffstat:
M
src/day09.lisp
 | 
44
+++++++++++++++++++++++++++-----------------
M
t/day09.lisp
 | 
18
++++++++++++++++--

2 files changed, 43 insertions(+), 19 deletions(-)
diff --git a/src/day09.lisp b/src/day09.lisp
@@ -1,5 +1,6 @@
 (defpackage #:adventofcode2022/day09
-  (:use #:cl #:adventofcode2022))
+  (:use #:cl #:adventofcode2022)
+  (:import-from #:alexandria #:clamp))
 (in-package #:adventofcode2022/day09)
 
 (defun move-head (head dir)
@@ -14,20 +15,11 @@
    (<= (abs (- (car head) (car tail))) 1)
    (<= (abs (- (cadr head) (cadr tail))) 1)))
 
-(defun move-tail (tail dir head)
-  (cond
-    ((char= dir #\U)
-     (setf (car tail) (car head))
-     (setf (cadr tail) (1+ (cadr head))))
-    ((char= dir #\D)
-     (setf (car tail) (car head))
-     (setf (cadr tail) (1- (cadr head))))
-    ((char= dir #\L)
-     (setf (car tail) (1+ (car head)))
-     (setf (cadr tail) (cadr head)))
-    ((char= dir #\R)
-     (setf (car tail) (1- (car head)))
-     (setf (cadr tail) (cadr head)))))
+(defun move-tail (tail head)
+  (incf (car tail)
+        (clamp (- (car head) (car tail)) -1 1))
+  (incf (cadr tail)
+        (clamp (- (cadr head) (cadr tail)) -1 1)))
 
 (defun task1 (inputs)
   (loop with visited-positions = (make-hash-table :test 'equal)
@@ -38,13 +30,31 @@
         do (loop for i from 1 to steps
                  do (move-head pos-head dir)
                  unless (head-tail-touching-p pos-head pos-tail)
-                   do (move-tail pos-tail dir pos-head)
+                   do (move-tail pos-tail pos-head)
                    and do (setf (gethash (copy-seq pos-tail) visited-positions) t))
         finally (return (hash-table-count visited-positions))))
 
+(defun task2 (inputs)
+  (loop with visited-positions = (make-hash-table :test 'equal)
+        with positions = (loop repeat 10 collect (list 0 0))
+        with pos-head = (car positions)
+        with pos-tail = (car (last positions))
+        initially (setf (gethash (list 0 0) visited-positions) t)
+        for (dir steps) in inputs
+        do (loop for i from 1 to steps
+                 do (move-head pos-head dir)
+                 do (loop with previous = pos-head
+                          for knot in (cdr positions)
+                          for i from 1
+                          unless (head-tail-touching-p previous knot)
+                            do (move-tail knot previous)
+                          do (setf previous knot))
+                 do (setf (gethash (copy-seq pos-tail) visited-positions) t))
+        finally (return (hash-table-count visited-positions))))
+
 (define-day 9
     (:translate-input (lambda (line)
                         (list (aref line 0)
                               (parse-integer (subseq line 2)))))
   #'task1
-  nil)
+  #'task2)
diff --git a/t/day09.lisp b/t/day09.lisp
@@ -1,6 +1,6 @@
 (in-package #:adventofcode2022/test)
 
-(defconstant +testdata-day09+ "R 4
+(defconstant +testdata-day09-task1+ "R 4
 U 4
 L 3
 D 1
@@ -9,9 +9,23 @@ D 1
 L 5
 R 2")
 
+(defconstant +testdata-day09-task2+ "R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20")
+
 (def-test day09-task1 ()
   (is-true
    (= 13
       (run-task 9 1
-                (make-string-input-stream +testdata-day09+)))))
+                (make-string-input-stream +testdata-day09-task1+)))))
 
+(def-test day09-task2 ()
+  (is-true
+   (= 36
+      (run-task 9 2
+                (make-string-input-stream +testdata-day09-task2+)))))