Add 2019 day 2 solutions

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diff --git a/2019/02/.gitignore b/2019/02/.gitignore
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+puzzle-[12].lisp
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diff --git a/2019/02/Makefile b/2019/02/Makefile
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+include ../../Makefiles/lisp.mk
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diff --git a/2019/02/puzzles.lisp b/2019/02/puzzles.lisp
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+#!/usr/bin/sbcl --script
+
+(load "../interpreter.lisp")
+
+(defun run-with-noun-and-verb (noun verb ram)
+  (setf (aref ram 1) noun
+        (aref ram 2) verb)
+  (intcode:run ram)
+  (aref ram 0))
+
+;; START PART 1
+(let ((program (intcode:parse "input")))
+  (format t "~d~%" (run-with-noun-and-verb 12 2 program)))
+;; END PART 1 START PART 2
+(let* ((program (intcode:parse "input"))
+       (ram (make-array (length program))))
+  (dotimes (noun 100)
+    (dotimes (verb 100)
+      (loop for i from 0 below (length program)
+            do (setf (aref ram i) (aref program i)))
+      (when (= (run-with-noun-and-verb noun verb ram) 19690720)
+        (format t "~d~%" (+ (* 100 noun) verb))
+        (quit)))))
+;; END PART 2
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diff --git a/2019/interpreter.lisp b/2019/interpreter.lisp
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+(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))))
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