1 files changed, 45 insertions, 0 deletions
diff --git a/2022/puzzle-8.lisp b/2022/puzzle-8.lisp
index 426ae13..38c5421 100644
--- a/2022/puzzle-8.lisp
+++ b/2022/puzzle-8.lisp
@@ -5,3 +5,48 @@
 (defparameter trees
   (mapcar (lambda (line) (mapcar (lambda (char) (parse-integer (string char))) (string-to-clist line)))
      lines))
+;; Size of a row or column
+(defparameter n-trees (length trees))
+
+(defun get-column (x)
+  (loop for row in trees
+        collect (nth x row)))
+
+(defun get-row (y)
+  (nth y trees))
+
+(defun get-tree (x y)
+  (nth x (nth y trees)))
+
+(defun is-visible? (x y)
+  (if (or (= x 0) (= x (- n-trees 1))
+         (= y 0) (= y (- n-trees 1)))
+      t
+      (let* ((tree (get-tree x y))
+             (lt-tree? (lambda (a) (< a tree)))
+             (row (get-row y))
+             (row-left (subseq row 0 x))
+             (row-right (subseq row (+ x 1)))
+             (col (get-column x))
+             (col-top (subseq col 0 y))
+             (col-bottom (subseq col (+ y 1))))
+        (or
+         (all lt-tree? row-left)
+         (all lt-tree? row-right)
+         (all lt-tree? col-top)
+         (all lt-tree? col-bottom)))))
+
+(defun how-many-visible ()
+  (loop
+    for x from 0 to (- n-trees 1)
+    sum
+    (reduce
+     #'+
+     (loop
+       for y from 0 to (- n-trees 1)
+       if (is-visible? x y)
+         collect 1
+       else
+         collect 0))))
+
+(format t "round 1: ~s~%" (how-many-visible))