6545da7f5f73

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/data/2021/17.txt	Fri Dec 17 20:45:15 2021 -0500
@@ -0,0 +1,1 @@
+target area: x=155..215, y=-132..-72

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/2021/days/day-17.lisp	Fri Dec 17 20:45:15 2021 -0500
@@ -0,0 +1,54 @@
+(advent:defpackage* :advent/2021/17 (:shadow x y))
+(in-package :advent/2021/17)
+
+(defstruct (p (:constructor p (&optional (x 0) (y 0))) (:conc-name nil))
+  (x 0 :type fixnum)
+  (y 0 :type fixnum))
+
+(defstruct (box (:constructor box (xmin xmax ymin ymax)) (:conc-name nil))
+  (xmin 0 :type fixnum)
+  (xmax 0 :type fixnum)
+  (ymin 0 :type fixnum)
+  (ymax 0 :type fixnum))
+
+(defun-inline pzerop (p) (and (zerop (x p)) (zerop (y p))))
+(defun-inline p->complex (p) (complex (x p) (y p)))
+(defun-inline p->char (p) (if (pzerop p) #\S #\#))
+(defun-inline in-box-p (p box)
+  (and (<= (xmin box) (x p) (xmax box))
+       (<= (ymin box) (y p) (ymax box))))
+
+(defun-inline step! (pos vel)
+  (incf (x pos) (x vel))
+  (incf (y pos) (y vel))
+  (decf (x vel) (signum (x vel)))
+  (decf (y vel)))
+
+(defun simulate (vel target)
+  (iterate (with v = (copy-p vel))
+           (with p = (p 0 0))
+           (step! p v)
+           (maximizing (y p) :into height)
+           (until (or (> (x p) (xmax target))
+                      (< (y p) (ymin target))))
+           (when (in-box-p p target)
+             (return height))))
+
+(defun solve (target)
+  (iterate (for vx :from 0 :to (xmax target))
+           (do-irange ((vy (ymin target) (- (ymin target))))
+             (for height = (simulate (p vx vy) target))
+             (when height
+               (maximizing height :into part1)
+               (counting t :into part2)))
+           (returning part1 part2)))
+
+(defun parse (stream &aux (line (read-line stream)))
+  (ppcre:register-groups-bind ((#'parse-integer xmin xmax ymin ymax))
+      ("target area: x=(-?\\d+)\\.\\.(-?\\d+), y=(-?\\d+)\\.\\.(-?\\d+)" line)
+    (box xmin xmax ymin ymax)))
+
+(define-problem (2021 17) (target parse) ()
+  (solve target))
+
+#; Scratch --------------------------------------------------------------------