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;; Example input: a-b,c-d which denotes [a,b] and [c,d]
;; We want to find if [c,d] < [a,b] or vice versa (complete inclusion)
;; and since we're working with integers, it's simply checking if the
;; bounds are included i.e. c in [a,b] and d in [a,b]
(defvar input (uiop:read-file-string "puzzle-4-input.txt"))
(defun parse-bound (str)
"Given STR=\"a-b\" return (a b)"
(let* ((sep (search "-" str))
(first (subseq str 0 sep))
(second (subseq str (+ sep 1))))
(list (parse-integer first) (parse-integer second))))
(defvar completed-parse
(with-input-from-string (s input)
(loop for line = (read-line s nil)
until (null line)
collect
;; given a-b,c-d we want ((a b) (c d))
(let* ((sep (search "," line))
(first-bound (subseq line 0 sep))
(second-bound (subseq line (+ sep 1))))
(list (parse-bound first-bound) (parse-bound second-bound))))))
(defun complete-inclusion (first-bound second-bound)
(destructuring-bind (a b) first-bound
(destructuring-bind (c d) second-bound
(or
(and
(>= a c) (<= a d)
(>= b c) (<= b d))
(and
(>= c a) (<= c b)
(>= d a) (<= d b))))))
(defvar round-1-answer (length (remove-if #'null
(mapcar (lambda (pair)
(destructuring-bind (first second) pair
(complete-inclusion first second)))
completed-parse))))
;; Round 2: any overlap at all. Basically just overhaul the inclusion
;; function and then do the same answer checking.
(defun any-inclusion (first second)
(destructuring-bind (a b) first
(destructuring-bind (c d) second
;; How about doing this through negation? [a,b] does not overlap with [c,d] at all if either b < c or a > d.
(not
(or
(< b c)
(> a d))))))
(defvar round-2-answer (length (remove-if #'null
(mapcar (lambda (pair)
(destructuring-bind (first second) pair
(any-inclusion first second)))
completed-parse))))
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