Fix Intcode bug (uninitialized memory was nil)

[adventofcode2019.git] / src / adventofcode2019 / intcode.clj

diff --git a/src/adventofcode2019/intcode.clj b/src/adventofcode2019/intcode.clj
index 252a6133350b88eb5836dc7c47279d2bd91c7ffd..dc542dd17e8240e49ca7a83efc950a092342ba38 100644 (file)
--- a/src/adventofcode2019/intcode.clj
+++ b/src/adventofcode2019/intcode.clj
@@ -9,10 +9,11 @@
         op (vec (drop 3 str-code))
         apply-flag (fn [flag arg]
                      (case flag
-                       \0 (fn ([S] (get-in S [:memory arg])) 
+                       ;; ORs avoid returning nil
+                       \0 (fn ([S] (or (get-in S [:memory arg]) 0)) 
                               ([_ _] arg))
                        \1 (constantly arg)
-                       \2 (fn ([S] (get-in S [:memory (+ arg (:relctr S))])) 
+                       \2 (fn ([S] (or (get-in S [:memory (+ arg (:relctr S))]) 0)) 
                               ([S _] (+ arg (:relctr S))))))
         with-flags (fn [f]
                      (fn [S & args]
@@ -21,20 +22,20 @@
       (case op
         [\0 \1] (fn [S a b c] ; ADD
                   (-> S 
-                      (assoc-in [:memory (c S 0)] (+' (a S) (b S)))
+                      (assoc-in [:memory (c S true)] (+' (a S) (b S)))
                       (update :ctr + 4)))
         [\0 \2] (fn [S a b c] ; MULT
                   (-> S
-                      (assoc-in [:memory (c S 0)] (*' (a S) (b S)))
+                      (assoc-in [:memory (c S true)] (*' (a S) (b S)))
                       (update :ctr + 4)))
         [\0 \3] (fn [S a _ _] ; IN
                   (-> S
-                      (assoc-in [:memory (a S 0)] (first (:input S)))
+                      (assoc-in [:memory (a S true)] (first (:input S)))
                       (update :input subvec 1)
                       (update :ctr + 2)))
         [\0 \4] (fn [S a _ _] ; OUT
                   (-> S
-                      (update :output conj (get-in S [:memory (a S 0)]))
+                      (update :output conj (or (get-in S [:memory (a S true)]) 0))
                       (update :ctr + 2))) 
         [\0 \5] (fn [S a b _] ; BNEQ
                    (update S :ctr (if (not= (a S) 0) (constantly (b S)) #(+ % 3))))
@@ -42,11 +43,11 @@
                    (update S :ctr (if (= (a S) 0) (constantly (b S)) #(+ % 3))))
         [\0 \7] (fn [S a b c] ; SLT
                   (-> S
-                      (assoc-in [:memory (c S 0)] (if (< (a S) (b S)) 1 0))
+                      (assoc-in [:memory (c S true)] (if (< (a S) (b S)) 1 0))
                       (update :ctr + 4)))
         [\0 \8] (fn [S a b c] ; SEQ
                   (-> S
-                      (assoc-in [:memory (c S 0)] (if (= (a S) (b S)) 1 0))
+                      (assoc-in [:memory (c S true)] (if (= (a S) (b S)) 1 0))
                       (update :ctr + 4)))
         [\0 \9] (fn [S a _ _] ; SREL
                    (-> S