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(ql:quickload '(fiveam str arrows transducers))
(defpackage #:day04
(:use #:cl #:fiveam)
(:local-nicknames (#:t #:transducers)))
(in-package #:day04)
(defparameter eg-input "Card 1: 41 48 83 86 17 | 83 86 6 31 17 9 48 53
Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
Card 3: 1 21 53 59 44 | 69 82 63 72 16 21 14 1
Card 4: 41 92 73 84 69 | 59 84 76 51 58 5 54 83
Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11")
(defun matching-numbers (line)
(destructuring-bind (_card winners haves)
(uiop:split-string line :separator '(#\: #\|))
(declare (ignorable _card))
(intersection
(mapcar #'parse-integer
(str:split " " winners :omit-nulls t))
(mapcar #'parse-integer
(str:split " " haves :omit-nulls t)))))
(defun solver1 (lines)
(t:transduce
(t:comp
(t:filter-map #'matching-numbers)
(t:map #'length)
(t:map #'1-)
(t:map (lambda (n) (expt 2 n))))
#'+
lines))
(defun solver1c (lines)
(arrows:->>
(mapcar #'matching-numbers lines)
(remove-if #'null)
(mapcar #'length)
(mapcar #'1-)
(mapcar (lambda (n) (expt 2 n)))
(apply #'+)))
(defun solver2 (lines)
(let* ((line-count (length lines))
(stash (make-hash-table :size line-count)))
(loop
for line in lines
for i from 0
for matches = (length (matching-numbers line))
do (incf (gethash i stash 0))
(dotimes (j matches)
(when (< (+ i j 1) line-count)
(incf (gethash (+ i j 1) stash 0)
(gethash i stash))))
sum (gethash i stash 0))))
(test solutions
(is (= 13 (solver1 (uiop:split-string eg-input :separator '(#\Newline)))))
(is (= 13 (solver1c (uiop:split-string eg-input :separator '(#\Newline)))))
(is (= 18619 (solver1 #p"input")))
(is (= 18619 (solver1c (uiop:read-file-lines "input"))))
(is (= 30 (solver2 (uiop:split-string eg-input :separator '(#\Newline)))))
(is (= 8063216 (solver2 (uiop:read-file-lines "input")))))
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