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(defvar %cave-hash% (hash))
(defstruct cave ()
name
neighbors
(:postinit (cv)
(assert cv.name)
(set [%cave-hash% cv.name] cv)))
(defstruct end-cave cave
(:method visit (cv path fn)
(push cv path)
[fn (remq t path)]))
(defstruct start-cave cave
(:method visit (cv path fn)
(unless (member cv path)
(push cv path)
(each ((n cv.neighbors))
n.(visit path fn)))))
(defstruct small-cave cave
(:method visit (cv path fn)
(let ((in-path (member cv path)))
(when (or (not in-path)
(not (member t path)))
(push cv path)
(if in-path
(push t path))
(each ((n cv.neighbors))
n.(visit path fn))))))
(defstruct big-cave cave
(:method visit (cv path fn)
(push cv path)
(each ((n cv.neighbors))
n.(visit path fn))))
(defun ensure-cave (name)
(or [%cave-hash% name]
(set [%cave-hash% name]
(match-case name
("end" (new end-cave name name))
("start" (new start-cave name name))
(@[all @str chr-islower] (new small-cave name name))
(@else (new big-cave name name))))))
(defun read-caves (: (name "input"))
(with-stream (s (open-file name))
(whilet ((line (get-line s)))
(match `@a-@b` line
(let ((ca (ensure-cave a))
(cb (ensure-cave b)))
(pushnew cb ca.neighbors)
(pushnew ca cb.neighbors))))))
(defun find-paths (fn)
(let ((start [%cave-hash% "start"]))
(assert start)
start.(visit nil fn)))
(defun solve (: (name "input"))
(let (paths)
(read-caves name)
(find-paths (opip reverse (mapcar .name) (push @1 paths)))
(mapdo [chain (ap join-with ",") pprinl] paths)
(len paths)))
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