88 lines
2.6 KiB
Common Lisp
88 lines
2.6 KiB
Common Lisp
(load "lib")
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(defparameter input (uiop:read-file-string "8-input"))
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(defparameter lines (get-lines input))
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;; Just converts every line into a sequence of integral digits
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(defparameter trees
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(mapcar (lambda (line) (mapcar (lambda (char) (parse-integer (string char))) (string-to-clist line)))
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lines))
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;; Size of a row or column
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(defparameter n-trees (length trees))
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(defun get-column (x)
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(loop for row in trees
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collect (nth x row)))
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(defun get-row (y)
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(nth y trees))
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(defun get-tree (x y)
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(nth x (nth y trees)))
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(defun at-end? (a)
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(or (= a 0) (= a (- n-trees))))
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(defun is-visible? (x y)
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(if (or (= x 0) (= x (- n-trees 1))
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(= y 0) (= y (- n-trees 1)))
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t
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(let* ((tree (get-tree x y))
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(lt-tree? (lambda (a) (< a tree)))
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(row (get-row y))
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(row-left (subseq row 0 x))
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(row-right (subseq row (+ x 1)))
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(col (get-column x))
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(col-top (subseq col 0 y))
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(col-bottom (subseq col (+ y 1))))
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(some #'identity
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(mapcar (lambda (x) (every lt-tree? x))
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(list row-left row-right col-top col-bottom))))))
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(defun how-many-visible ()
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(loop
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for x from 0 below n-trees
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sum
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(reduce
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#'+
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(loop
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for y from 0 below n-trees
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if (is-visible? x y)
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collect 1
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else
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collect 0))))
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(format t "round 1: ~s~%" (how-many-visible))
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(defun keep-till-last-satisfying (pred lst &optional acc)
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"Iteratively collect all items of LST that satisfy PRED, including the
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first member which does not satisfy PRED."
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(cond
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((null lst) acc)
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((not (funcall pred (car lst)))
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(cons (car lst) acc))
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(t
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(keep-till-last-satisfying pred (cdr lst) (cons (car lst) acc)))))
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(defun scenic-score (x y)
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"Calculate the scenic score of the tree at position X, Y."
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(let* ((tree (get-tree x y))
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(lt-tree? (lambda (a) (< a tree)))
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(row (get-row y))
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(row-left (reverse (subseq row 0 x)))
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(row-right (subseq row (+ x 1)))
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(col (get-column x))
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(col-top (reverse (subseq col 0 y)))
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(col-bottom (subseq col (+ y 1))))
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(reduce #'*
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(mapcar (lambda (x) (length (keep-till-last-satisfying lt-tree? x)))
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(list row-left row-right col-top col-bottom)))))
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(format t "round 2: ~s~%"
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(car (sort
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;; Calculate all scenic scores
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(loop for x from 0 below n-trees
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nconcing
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(loop for y from 0 below n-trees
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collect
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(scenic-score x y)))
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#'>)))
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