0a241f64eebb

--- a/advent.asd	Fri Dec 06 18:58:39 2019 -0500
+++ b/advent.asd	Fri Dec 06 20:57:40 2019 -0500
@@ -41,6 +41,8 @@
                (:file "package")
                (:module "src" :serial t
                 :components ((:file "utils")
+                             (:module "2016" :serial t
+                              :components ((:auto-module "days")))
                              (:module "2017" :serial t
                               :components ((:file "number-spiral")
                                            (:file "knot-hash")

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/data/2016/01.txt	Fri Dec 06 20:57:40 2019 -0500
@@ -0,0 +1,1 @@
+R1, L3, R5, R5, R5, L4, R5, R1, R2, L1, L1, R5, R1, L3, L5, L2, R4, L1, R4, R5, L3, R5, L1, R3, L5, R1, L2, R1, L5, L1, R1, R4, R1, L1, L3, R3, R5, L3, R4, L4, R5, L5, L1, L2, R4, R3, R3, L185, R3, R4, L5, L4, R48, R1, R2, L1, R1, L4, L4, R77, R5, L2, R192, R2, R5, L4, L5, L3, R2, L4, R1, L5, R5, R4, R1, R2, L3, R4, R4, L2, L4, L3, R5, R4, L2, L1, L3, R1, R5, R5, R2, L5, L2, L3, L4, R2, R1, L4, L1, R1, R5, R3, R3, R4, L1, L4, R1, L2, R3, L3, L2, L1, L2, L2, L1, L2, R3, R1, L4, R1, L1, L4, R1, L2, L5, R3, L5, L2, L2, L3, R1, L4, R1, R1, R2, L1, L4, L4, R2, R2, R2, R2, R5, R1, L1, L4, L5, R2, R4, L3, L5, R2, R3, L4, L1, R2, R3, R5, L2, L3, R3, R1, R3

--- a/package.lisp	Fri Dec 06 18:58:39 2019 -0500
+++ b/package.lisp	Fri Dec 06 20:57:40 2019 -0500
@@ -33,6 +33,7 @@
     :positions-if
     :digits
     :fresh-vector
+    :first-character
     :let-result
     :let-complex
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/2016/days/day-01.lisp	Fri Dec 06 20:57:40 2019 -0500
@@ -0,0 +1,26 @@
+(defpackage :advent/2016/01 #.cl-user::*advent-use*)
+(in-package :advent/2016/01)
+
+
+(defun turn (direction heading)
+  (* heading (ecase direction
+               (#\L #c(0 1))
+               (#\R #c(0 -1)))))
+
+(define-problem (2016 1) (data read-line) (298 158)
+  (iterate
+    (with pos = #c(0 0))
+    (with seen = (make-hash-set :initial-contents (list #c(0 0))))
+    (for ((#'first-character direction) (#'parse-integer distance))
+         :matching "([LR])(\\d+)" :against data)
+    (for heading :seed #c(0 1) :then (turn direction heading))
+    (do-repeat distance
+      (incf pos heading)
+      (finding-first pos :such-that (hset-contains-p seen pos) :into part2)
+      (hset-insert! seen pos))
+    (returning (manhattan-distance pos)
+               (manhattan-distance part2))))
+
+
+#; Scratch --------------------------------------------------------------------
+

--- a/src/2017/days/day-03.lisp	Fri Dec 06 18:58:39 2019 -0500
+++ b/src/2017/days/day-03.lisp	Fri Dec 06 20:57:40 2019 -0500
@@ -2,12 +2,6 @@
 (in-package :advent/2017/03)
 
 
-(defun manhattan-distance (a b)
-  (let-complex ((ax ay a)
-                (bx by b))
-    (+ (abs (- ax bx))
-       (abs (- ay by)))))
-
 (defun neighbors (coord)
   (iterate (for (dx dy) :within-radius 1 :skip-origin t)
            (collect (+ coord (complex dx dy)))))

--- a/src/2019/days/day-03.lisp	Fri Dec 06 18:58:39 2019 -0500
+++ b/src/2019/days/day-03.lisp	Fri Dec 06 20:57:40 2019 -0500
@@ -20,15 +20,11 @@
         (princ (gethash (complex x y) grid #\.)))
       (terpri))))
 
-(defun first-character (string)
-  (aref string 0))
-
 (defun parse-path (string)
-  (gathering
-    (ppcre:do-register-groups
-        ((#'first-character direction) (#'parse-integer distance))
-        ("([UDLR])(\\d+)" string)
-      (gather (cons direction distance)))))
+  (iterate
+    (for ((#'first-character direction) (#'parse-integer distance))
+         :matching "([UDLR])(\\d+)" :against string)
+    (collect (cons direction distance))))
 
 (defun delta (direction)
   (ecase direction

--- a/src/utils.lisp	Fri Dec 06 18:58:39 2019 -0500
+++ b/src/utils.lisp	Fri Dec 06 20:57:40 2019 -0500
@@ -32,6 +32,9 @@
       (symbol (alexandria:make-keyword input))
       (string (alexandria:make-keyword (string-upcase (str:trim input)))))))
 
+(defun ensure-list (input)
+  (if (listp input) input (list input)))
+
 
 ;;;; Problems -----------------------------------------------------------------
 (defmacro define-problem-tests ((year day) part1 part2)
@@ -72,7 +75,6 @@
     :type "txt"))
 
 
-
 ;;;; Readers ------------------------------------------------------------------
 (defun read-numbers-from-string (line)
   (mapcar #'parse-integer (ppcre:all-matches-as-strings "-?\\d+" line)))
@@ -227,11 +229,6 @@
                (return start)))))
 
 
-;;;; Iterate ------------------------------------------------------------------
-(defmacro returning (&rest values)
-  `(finally (return (values ,@values))))
-
-
 ;;;; Miscellaneous ------------------------------------------------------------
 (defun hash-table= (h1 h2 &optional (test #'eql))
   "Return whether `h1` and `h2` have the same keys and values.
@@ -434,6 +431,11 @@
     (coerce sequence 'vector)))
 
 
+(defun first-character (string)
+  "Return the first character of `string`."
+  (char string 0))
+
+
 (defmacro let-result ((symbol initform) &body body)
   "Bind `symbol` to initform, execute `body`, and return `symbol`.