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#!/usr/bin/sbcl --script
(defun main (filename)
(loop with lines = (read-file-to-lines filename)
with dimensions = (array-dimensions lines)
for i from 0 below (first dimensions)
sum (loop for j from 0 below (second dimensions)
when (char= #\0 (aref lines i j))
sum (score-for-trail-head lines i j))))
(defun read-file-to-lines (filename)
(with-open-file (stream filename)
(let ((lines (loop for line = (read-line stream nil)
while line
collect (coerce line 'array))))
(make-array (list (length lines)
(length (first lines)))
:initial-contents lines))))
(defun score-for-trail-head (lines i j)
(let* ((positions (positions-of-nines lines i j))
;; START PART 1
(positions (remove-duplicates positions :test 'equal))
;; END PART 1
)
(length positions)))
(defun positions-of-nines (lines i j)
(let ((char (aref lines i j)))
(if (char= #\9 char)
(list (cons i j))
(loop with needs = (code-char (1+ (char-code char)))
with dimensions = (array-dimensions lines)
for (i . j) in (list (cons (1- i) j) (cons i (1- j))
(cons (1+ i) j) (cons i (1+ j)))
if (and (< -1 i (first dimensions))
(< -1 j (second dimensions))
(char= (aref lines i j) needs))
append (positions-of-nines lines i j)))))
(format t "~d~%" (main "input"))
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