advent-2025/p3/p3.org

Solution to p3

First load the data as a list of lists of numbers

  (with-temp-buffer
    (insert-file-contents "input")
    (advent/replace-multiple-regex-buffer
     '(("\\(.\\)" . "\\1 ")
       ("^" . "(")
       ("$" . ")")))
    (goto-char (point-min))
    (insert "(setq data '(")
    (goto-char (point-max))
    (insert "))")
    (eval-buffer))

This is for part 1:

  (defun joltage (bank)
    (let* ((max-joltage (-max bank))
           (max-pos (1+ (-elem-index max-joltage bank))))
      (if (< max-pos (length bank))
          (+ (* 10 max-joltage) (-max (-drop max-pos bank)))
        (+ (* 10 (-max (-drop-last 1 bank))) max-joltage))))

  (-sum (-map #'joltage data))

17405

Let us redo it with a recursive approach

  (setq max-batteries 12)

  (defun joltage (bank no-batteries)
    (if (< no-batteries 0) 0
      (let ((mult (expt 10 no-batteries))
            (max-available-joltage (-max (-drop-last no-batteries bank))))
        (+ (* mult max-available-joltage)
           (joltage (-drop (1+ (-elem-index max-available-joltage bank)) bank)
                    (- no-batteries 1))))))

  (-sum (--map (joltage it (- max-batteries 1)) data))

171990312704598