Add 2019 day 2 solutions

1 files changed, 56 insertions, 0 deletions

diff --git a/2019/interpreter.lisp b/2019/interpreter.lisp
new file mode 100644
index 0000000..30bee82
--- /dev/null
+++ b/2019/interpreter.lisp
@@ -0,0 +1,56 @@
+(defpackage #:intcode
+  (:use :cl)
+  (:export :run :parse))
+
+(in-package #:intcode)
+
+;;; Interpreter
+
+(defun run (ram)
+  (let ((ip 0))
+    (loop
+     (let ((opcode (aref ram ip))
+           (arg-1 (try-aref ram (+ ip 1)))
+           (arg-2 (try-aref ram (+ ip 2)))
+           (arg-3 (try-aref ram (+ ip 3))))
+       (case opcode
+         (1
+          (setf (aref ram arg-3)
+                (+ (aref ram arg-1)
+                   (aref ram arg-2))))
+         (2
+          (setf (aref ram arg-3)
+                (* (aref ram arg-1)
+                   (aref ram arg-2))))
+         (99
+          (return-from run))
+         (otherwise
+          (error (format nil "Invalid opcode ‘~d’" opcode)))))
+     (incf ip 4))))
+
+;;; Input Parsing
+
+(defun parse (filename)
+  (with-open-file (stream filename)
+    (let ((contents (make-string (file-length stream))))
+      (read-sequence contents stream)
+      (extract-numbers-from-string contents))))
+
+(defun extract-numbers-from-string (string)
+  (loop for comma-pos = (position-if #'commap string)
+        collect (parse-integer (subseq string 0 comma-pos)) into numbers
+        unless comma-pos
+          return (coerce numbers 'vector)
+        do (setq string (subseq string (1+ comma-pos)))))
+
+;;; Helper Functions
+
+(defun commap (char)
+  (char= char #\,))
+
+(defun try-aref (array &rest subscripts)
+  (loop for i in subscripts
+        for j in (array-dimensions array)
+        unless (< -1 i j)
+          return nil
+        finally (return (apply #'aref array subscripts))))
\ No newline at end of file