(defun build-count-hash (lines)
  (let ((hash (make-hash-table :test 'equal)))
    (dolist (line lines) (expand-line line hash))
    hash))

(defun mark-lines (lines hash)
  (dolist (line lines) (expand-line line hash)))

(defun count-crossing-points (lines)
  (let ((count-hash (build-count-hash lines)))
    (loop for k being the hash-keys in count-hash using (hash-value v)
          count (>= v 2))))

(defun reverse-partition (pred col)
  (loop with yays = '()
        with nays = '()
        for e in col
        do (if (funcall pred e)
               (setf yays (cons e yays))
               (setf nays (cons e nays)))
        finally (return (list yays nays))))

(defun part1 (input)
  (count-crossing-points (remove-if #'angled-line-p input)))
(defun part2 (input)
  (count-crossing-points input))
(format t "===== Part 1 =====")
(format t "Result: ~A~%~%" (time (part1 *data*)))

(defun count-crossing-points (lines count-hash)
  (mark-lines lines count-hash)
  (loop for k being the hash-keys in count-hash using (hash-value v)
        count (>= v 2)))

(format t "===== Part 2 =====")
(format t "Result: ~A~%" (time (part2 *data*)))

(time
 (let ((hash (make-hash-table :test 'equal))
       (lines (reverse-partition #'angled-line-p *data*)))
   (format t "Part 1: ~A~%" (count-crossing-points (cadr lines) hash))
   (format t "Part 2: ~A~%" (count-crossing-points (car lines) hash))))