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(ql:quickload '(fiveam str))
(defparameter eg-input "seeds: 79 14 55 13
seed-to-soil map:
50 98 2
52 50 48
soil-to-fertilizer map:
0 15 37
37 52 2
39 0 15
fertilizer-to-water map:
49 53 8
0 11 42
42 0 7
57 7 4
water-to-light map:
88 18 7
18 25 70
light-to-temperature map:
45 77 23
81 45 19
68 64 13
temperature-to-humidity map:
0 69 1
1 0 69
humidity-to-location map:
60 56 37
56 93 4")
(defun parse-rules (rule)
(destructuring-bind (dest source span) rule
(list source (+ source span) (- dest source))))
(defun translate (rules value)
(dolist (rule rules)
(destructuring-bind (start end offset) rule
(when (<= start value (1- end))
(return-from translate (+ value offset)))))
value)
(defun transformation-in-order-p (names)
(loop for (one two) on names
for start = (cadr (str:split "-TO-" (symbol-name one)))
for end = (car (str:split "-TO-" (symbol-name two)))
always (or (string-equal start end) (null two))))
(fiveam:test parts
(let ((rules (mapcar #'parse-rules '((50 98 2) (52 50 48)))))
(fiveam:is (= 9 (translate rules 9)))
(fiveam:is (= 61 (translate rules 59)))
(fiveam:is (= 51 (translate rules 99))))
(fiveam:is-true
(transformation-in-order-p '(a-to-b b-to-c c-to-goal))))
(defun parser (lines)
(let (seeds
maps-stack
(translators (make-hash-table)))
(dolist (line lines)
(cond
((str:emptyp line))
((str:starts-with? "seeds:" line)
(setf seeds
(mapcar #'parse-integer (cdr (str:split-omit-nulls #\Space line)))))
((str:ends-with-p "map:" line)
(push (read-from-string line) maps-stack))
((push (parse-rules (mapcar #'parse-integer (str:split-omit-nulls #\Space line)))
(gethash (car maps-stack) translators)))))
(loop for rule-name being the hash-key of translators do
(setf (gethash rule-name translators)
(sort (gethash rule-name translators) #'< :key #'car)))
(setf maps-stack (nreverse maps-stack))
(transformation-in-order-p maps-stack)
(values maps-stack translators seeds)))
(defun translate-range (rules ranges &optional translated-ranges)
"It assumes rules are in order."
(if (or (endp rules) (endp ranges))
(sort (append ranges translated-ranges) #'< :key #'car)
(destructuring-bind (rule-start rule-end rule-offset) (car rules)
(destructuring-bind (element-start element-end) (car ranges)
(cond
;; element right sided to rule range thus move to next rule
((<= rule-end element-start)
(translate-range (cdr rules) ranges translated-ranges))
;; element is left sided to rule, thus identity map the range
((<= element-end rule-start)
(translate-range rules
(cdr ranges)
(cons (car ranges) translated-ranges)))
;; element range is fully contained, thus map offset
((<= rule-start element-start element-end rule-end)
(translate-range rules
(cdr ranges)
(cons (list (+ rule-offset element-start)
(+ rule-offset element-end))
translated-ranges)))
;; element overlaps on the left of range, thus slice it,
;; identity map first part, pass the overlap for it to translate on next level
((< element-start rule-start)
(translate-range rules
(cons (list rule-start element-end)
(cdr ranges))
(cons (list element-start rule-start)
translated-ranges)))
;; element overlaps on the right of the range, thus slice it,
;; offset map first part, transfer remainder for next rule
((< rule-end element-end)
(translate-range (cdr rules)
(cons (list rule-end element-end)
(cdr ranges))
(cons (list (+ rule-offset element-start)
(+ rule-offset rule-end))
translated-ranges)))
((assert nil nil "Not all cases processed")))))))
(fiveam:test range-translation
(let ((single-rule '((5 10 3))))
(fiveam:is (equal '((16 18)) (translate-range single-rule '((16 18))))
"Right sided element")
(fiveam:is (equal '((1 4)) (translate-range single-rule '((1 4))))
"Left sided element")
(fiveam:is (equal '((9 11)) (translate-range single-rule '((6 8))))
"Fully contained")
(fiveam:is (equal '((3 5) (8 10)) (translate-range single-rule '((3 7))))
"Left overlap")
(fiveam:is (equal '((10 13) (12 13)) (translate-range single-rule '((9 13))))
"Right overlap")))
(defun translator (translate-chain translator-rules)
(lambda (value)
(reduce
(lambda (acc fn)
(translate (gethash fn translator-rules) acc))
translate-chain
:initial-value value)))
(defun solver1 (lines)
(multiple-value-bind (maps-stack translator seeds) (parser lines)
(apply #'min (mapcar (translator maps-stack translator) seeds))))
(defun seed-to-ranges (seeds)
(arrows:->
(loop for (start span) on seeds by #'cddr
collect (list start (+ start span)))
(sort #'< :key #'car)))
(defun solver2 (lines)
(multiple-value-bind (maps-stack translator seeds) (parser lines)
(caar
(reduce
(lambda (acc fn)
(translate-range (gethash fn translator) acc))
maps-stack
:initial-value (seed-to-ranges seeds)))))
(fiveam:test solutions
(fiveam:is
(= 35
(solver1
(uiop:split-string eg-input :separator '(#\Newline)))))
(fiveam:is
(= 46
(solver2
(uiop:split-string eg-input :separator '(#\Newline)))))
(fiveam:is
(= 662197086
(solver1
(uiop:read-file-lines "input"))))
(fiveam:is
(= 52510809
(solver2
(uiop:read-file-lines "input")))))
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