61 lines
1.8 KiB
Common Lisp
61 lines
1.8 KiB
Common Lisp
(defun read-data (path)
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(with-open-file (stream path)
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(loop for line = (read-line stream nil)
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while line collect line)))
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(defparameter *input-source*
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(cadr *posix-argv*))
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;; Useful in testing
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;; (defparameter *input-source* "example_input")
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;; (defparameter *input-source* "input")
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(defparameter *data*
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(coerce (read-data *input-source*) 'vector))
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(defun most-common (data column)
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(loop for row across data
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counting (char= #\0 (aref row column)) into zeroes
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counting (char= #\1 (aref row column)) into ones
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finally (return (if (> zeroes ones) #\0 #\1))))
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(defun least-common (data column)
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(invert-bit (most-common data column)))
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(defun invert-bit (bit)
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(if (char= bit #\0) #\1 #\0))
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(defun invert (bits)
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(map 'string #'invert-bit bits))
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(defun gamma-rate (data)
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(loop for column from 0 below (length (aref data 0))
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collect (most-common data column)))
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(defun parse-bitfield (bits)
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(parse-integer (coerce bits 'string) :radix 2))
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(defun part1 (data)
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(let ((gamma-bits (gamma-rate data)))
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(* (parse-bitfield gamma-bits)
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(parse-bitfield (invert gamma-bits)))))
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(defun with-bit-at-position (data position bit)
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(remove-if-not (lambda (row) (char= (aref row position) bit))
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data))
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(defun part2-filter (data &key (most-common-f #'most-common))
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(loop for d = data then (with-bit-at-position d column (funcall most-common-f d column))
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for column from 0 below (length (aref data 0))
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until (= 1 (length d))
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finally (return (aref d 0))))
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(defun part2 (data)
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(let ((oxygen (part2-filter data))
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(co2 (part2-filter data :most-common-f #'least-common)))
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(* (parse-bitfield oxygen)
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(parse-bitfield co2))))
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(format t "Part 1: ~A~%" (part1 *data*))
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(format t "Part 2: ~A~%" (part2 *data*))
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