Day 19

Added solution for day 19. Adapted day16 a bit on the way.

advent-of-code-2018.asd

@@ -24,4 +24,6 @@
                (:file "day13")
                (:file "day14")
                (:file "day16")
-               (:file "day17")))
+               (:file "day17")
+               (:file "day18")
+               (:file "day19")))

day16.lisp

@@ -2,20 +2,28 @@
 
 (in-package :advent-of-code-2018)
 
+(defun day16-make-test-case (line1 line2 line3)
+  (let ((before (extract-integers line1))
+        (instruction (extract-integers line2))
+        (after (extract-integers line3)))
+    (list (make-array (length before) :initial-contents before)
+          instruction
+          (make-array (length after) :initial-contents after))))
+
 (defun day16-parse-input ()
   (with-open-file (in (puzzlepath "input16.txt"))
     (loop :for line := (read-line in nil)
           :while line
           :unless (= 0 (length line))
           :when (char= #\B (char line 0))
-          :collect (mapcar #'extract-integers (list line (read-line in) (read-line in))) :into test-cases
+          :collect (day16-make-test-case line (read-line in) (read-line in)) :into test-cases
           :else :collect (extract-integers line) :into test-prog
           :finally (return (list test-cases test-prog)))))
 
 (defun day16-execute! (register command)
   (destructuring-bind (cmd inp1 inp2 out) command
     (macrolet ((reg (x)
-                 `(nth ,x register)))
+                 `(aref register ,x)))
       (setf (reg out)
             (case cmd
               (addr (+ (reg inp1) (reg inp2)))
@@ -65,7 +73,8 @@
           :count (<= 3 (length (day16-test-case case))) :into count
           :finally (format t "There are ~a test cases with 3 or more possible instructions.~%" count))
     (loop :with id->opcode := (day16-construct-opcode-ids cases)
-          :with registers := (list 0 0 0 0)
+          :with registers := #(0 0 0 0)
           :for (id . args) :in prog
           :do (setf registers (day16-execute! registers (cons (aref id->opcode id) args)))
-          :finally (format t "After executing the test program the value in register 0 is ~a.~%" (first registers)))))
+          :finally (format t "After executing the test program the value in register 0 is ~a.~%"
+                           (aref registers 0)))))

day19.lisp

@@ -0,0 +1,63 @@
+;;;; day19.lisp
+
+(in-package :advent-of-code-2018)
+
+(defstruct (program-state (:conc-name pstate-))
+  instructions
+  (ip 0)
+  (ip-binding nil)
+  (registers (make-array 6 :initial-element 0 :element-type 'integer)))
+
+(defun day19-parse-input (&optional (file (puzzlepath "input19.txt")))
+  (loop-line-by-line file
+    :when (char= #\# (char line 0)) :collect (list 'ip (parse-integer line :start 4))
+    :else :collect (cons (read-from-string line) (extract-integers line))))
+
+(defun day19-initialize-program (instruction-list)
+  (make-program-state :instructions (make-array (1- (length instruction-list))
+                                                :initial-contents (rest instruction-list))
+                      :ip-binding (second (first instruction-list))))
+
+(defun day19-execute! (program-state)
+  (with-accessors ((instr pstate-instructions)
+                   (ip pstate-ip)
+                   (ip-binding pstate-ip-binding)
+                   (registers pstate-registers))
+      program-state
+    (when ip-binding
+      (setf (aref registers ip-binding) ip))
+    ;(format t "before: ~a~%" registers)
+    (let ((command  (aref instr ip)))
+      (if (eq 'ip (first command))
+          (setf ip-binding (second command))
+          (day16-execute! registers command))
+     ; (format t "command: ~a~%~%" command)
+      )
+    (when ip-binding
+      (setf ip (aref registers ip-binding)))
+    (incf ip)
+    (< -1 ip (length instr))))
+
+;;; runs FOREVER
+(defun day19-brute-force ()
+  (loop :with prog := (day19-initialize-program (day19-parse-input))
+        :count t :into loops
+        :while (day19-execute! prog)
+        :finally (format t "The first background process exits with the value ~a in the zeroth register.~%"
+                         (aref (pstate-registers prog) 0)))
+  (let ((prog (day19-initialize-program (day19-parse-input))))
+    (setf (aref (pstate-registers prog) 0) 1)
+    (loop :while (day19-execute! prog)
+          :finally
+          (format t "The second background process exits with the value ~a in the zeroth register.~%"
+                  (aref (pstate-registers prog) 0)))))
+
+(defun day19-analytic (input)
+  (loop :for a :from 1 :upto (ceiling (sqrt input))
+        :when (= 0 (mod input a)) :sum (+ a (/ input a))))
+
+(defun day19 ()
+  (format t "The first background process exits with the value ~a in the zeroth register.~%"
+          (day19-analytic 931))
+  (format t "The second background process exits with the value ~a in the zeroth register.~%"
+          (day19-analytic 10551331)))