63 lines
2.2 KiB
EmacsLisp
63 lines
2.2 KiB
EmacsLisp
;; Advent of Code 2020 - Day
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(require 'cl-lib)
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(require 'dash)
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(require 'f)
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(require 's)
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(setq day8/input
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(apply #'vector
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(-map (lambda (s)
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(pcase-let ((`(,op ,val) (s-split " " s t)))
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(cons (intern op) (string-to-number val))))
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(s-lines (s-chomp (f-read "/tmp/aoc/day8.txt"))))))
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(defun day8/step (code position acc)
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(if (>= position (length code))
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(cons 'final acc)
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(let ((current (aref code position)))
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(aset code position :done)
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(pcase current
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(:done (cons 'loop acc))
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(`(nop . ,val) (cons (+ position 1) acc))
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(`(acc . ,val) (cons (+ position 1) (+ acc val)))
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(`(jmp . ,val) (cons (+ position val) acc))))))
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;; Puzzle 1
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(message "Solution to day8/1: %s"
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(let ((code (copy-sequence day8/input))
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(position 0)
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(acc 0))
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(cl-loop for next = (day8/step code position acc)
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when (equal 'loop (car next)) return (cdr next)
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do (setq position (car next))
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do (setq acc (cdr next)))))
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;; Puzzle 2
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(defun day8/flip-at (code pos)
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(pcase (aref code pos)
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(`(nop . ,val) (aset code pos `(jmp . ,val)))
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(`(jmp . ,val) (aset code pos `(nop . ,val)))
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(other (error "Unexpected flip op: %s" other))))
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(defun day8/try-flip (flip-at code position acc)
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(day8/flip-at code flip-at)
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(cl-loop for next = (day8/step code position acc)
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when (equal 'loop (car next)) return nil
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when (equal 'final (car next)) return (cdr next)
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do (setq position (car next))
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do (setq acc (cdr next))))
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(message "Solution to day8/2: %s"
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(let ((flip-options (cl-loop for op being the elements of day8/input
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using (index idx)
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for opcode = (car op)
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when (or (equal 'nop opcode)
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(equal 'jmp opcode))
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collect idx)))
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(cl-loop for flip-at in flip-options
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for result = (day8/try-flip flip-at (copy-sequence day8/input) 0 0)
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when result return result)))
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