day 8 in common lisp

common-lisp/day-8/example.txt

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+../../input/day-8-example.txt

common-lisp/day-8/input.txt

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+../../input/day-8.txt

common-lisp/day-8/solution.lisp

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+#!/usr/bin/env -S sbcl --script
+
+;; Copyright (C) 2022
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+(require 'asdf)
+(require 'uiop)
+(require 'str)
+(require 'iterate)
+
+(defpackage :advent-of-code-day-8
+  (:use :cl :iterate))
+
+(in-package :advent-of-code-day-8)
+
+(defclass tree ()
+  ((x
+    :initarg :x
+    :reader x)
+   (y
+    :initarg :y
+    :reader y)))
+
+(defmacro make-tree (x y)
+  `(make-instance 'tree :x ,x :y ,y))
+
+(defun scan-right? (trees position)
+  (iter (with width = (- (array-dimension trees 1) 1))
+        (with tree-height = (aref trees (y position) (x position)))      
+        (for i from (+ (x position) 1) to width)
+        (for tree = (aref trees (y position) i))
+        (counting t into view-count)
+        (unless (< tree tree-height)
+          (return (cons :not-visible view-count)))
+        (finally (return (cons :visible view-count)))))
+
+(defun scan-left? (trees position)
+  (iter (with tree-height = (aref trees (y position) (x position)))
+        (for i from (- (x position) 1) downto 0)
+        (for tree = (aref trees (y position) i))    
+        (counting t into view-count)
+        (unless (< tree tree-height)
+          (return (cons :not-visible view-count)))
+        (finally (return (cons :visible view-count)))))
+
+(defun scan-down? (trees position)
+  (iter (with height = (- (array-dimension trees 0) 1))
+        (with tree-height = (aref trees (y position) (x position)))
+        (for i from (+ (y position) 1) to height)
+        (for tree = (aref trees i (x position)))
+        (counting t into view-count)
+        (unless (< tree tree-height)
+          (return (cons :not-visible view-count)))
+        (finally (return (cons :visible view-count)))))
+
+(defun scan-up? (trees position)
+  (iter (with tree-height = (aref trees (y position) (x position)))
+        (for i from (- (y position) 1) downto 0)
+        (for tree = (aref trees i (x position)))
+        (counting t into view-count)
+        (unless (< tree tree-height)
+          (return (cons :not-visible view-count)))
+        (finally (return (cons :visible view-count)))))
+
+(defun tree-visible? (trees position)
+  (or (equal (car (scan-right? trees position)) :visible)
+      (equal (car (scan-left? trees position)) :visible)
+      (equal (car (scan-down? trees position)) :visible)
+      (equal (car (scan-up? trees position)) :visible)))
+
+(defun scenic-score (trees tree)
+  (* (cdr (scan-right? trees tree))
+     (cdr (scan-left? trees tree))
+     (cdr (scan-down? trees tree))
+     (cdr (scan-up? trees tree))))
+
+(defun trees-from-file-lines (lines)
+  (let* ((split-lines-into-digits (mapcar (lambda (line)
+                                            (str:split "" line :omit-nulls t))
+                                          lines))
+         (numbers (mapcar (lambda (row)
+                            (mapcar 'parse-integer row))
+                          split-lines-into-digits))
+         (x (length (nth 0 numbers)))
+         (y (length numbers)))
+    (make-array (list x y) :initial-contents numbers)))
+
+(defun solution-part-1 (trees)
+  (iter (with width = (- (array-dimension trees 1) 1))
+        (with height = (- (array-dimension trees 0) 1))
+        (for y from 1 to (- height 1))
+        (sum (iter (for x from 1 to (- width 1))
+                   (for tree = (make-instance 'tree :x x :y y))
+                   (counting (tree-visible? trees tree)))
+             into visible-interior-trees)
+        (finally (return (+ visible-interior-trees (* width 2) (* height 2))))))
+
+(defun solution-part-2 (trees)
+  (iter (with width = (- (array-dimension trees 1) 1))
+        (with height = (- (array-dimension trees 0) 1))
+        (for y from 1 to (- height 1))
+        (appending (iter (for x from 1 to (- width 1))
+                         (for tree = (make-instance 'tree :x x :y y))
+                         (collect (scenic-score trees tree)))
+                   into scores)
+        (finally (return (let* ((sorted-scores (sort scores '>)))
+                           (car sorted-scores))))))
+
+(let ((trees (trees-from-file-lines (uiop:read-file-lines "example.txt"))))
+  (assert (= 21 (solution-part-1 trees))))
+
+(let ((trees (trees-from-file-lines (uiop:read-file-lines "input.txt"))))
+  (assert (= 1736 (solution-part-1 trees))))
+
+(let ((trees (trees-from-file-lines (uiop:read-file-lines "example.txt"))))
+  (assert (= 8 (solution-part-2 trees))))
+
+(let ((trees (trees-from-file-lines (uiop:read-file-lines "input.txt"))))
+  (assert (= 268800 (solution-part-2 trees))))
+
+;; Local Variables:
+;; mode: lisp
+;; End:

input/day-8-example.txt

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