1 files changed, 54 insertions, 0 deletions
diff --git a/puzzle-2.lisp b/puzzle-2.lisp
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+++ b/puzzle-2.lisp
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+(defvar input (uiop:read-file-string "puzzle-2-input.txt"))
+;; Each newline represents a new round, which we should parse on the go
+
+(defun sensible-convert-input (str)
+  (cond
+    ((or (string= str "X") (string= str "A")) 0)
+    ((or (string= str "Y") (string= str "B")) 1)
+    ((or (string= str "Z") (string= str "C")) 2)))
+
+;; Round 1
+(defvar rounds
+  (with-input-from-string (stream input)
+    (loop
+      for strategy = (read-line stream nil)
+      until (null strategy)
+      collect
+      (let ((opponent (subseq strategy 0 1))
+            (yours (subseq strategy 2 3)))
+        (list (sensible-convert-input opponent) (sensible-convert-input yours))))))
+
+(loop
+  for round in rounds
+  until (null round)
+  sum
+  (destructuring-bind (opp you) round
+    (+
+     1 you ;; base score
+     (cond  ; outcome score
+       ((eq you opp) 3)
+       ((eq (mod (+ 1 opp) 3) you) 6)
+       (t 0)))))
+
+;; Round 2.
+
+;; We can still use the same rounds data as previously, just
+;; reinterpret it in when doing the sum.
+
+(defun get-correct-choice (opponent outcome)
+  (case outcome
+    (0 (mod (- opponent 1) 3))
+    (1 opp)
+    (2 (mod (+ 1 opponent) 3))
+    (t 0)))
+
+(loop for round in rounds
+      sum
+      (destructuring-bind (opp you) round
+        (let ((choice (get-correct-choice opp you)))
+          (+ 1 choice
+             (case you ;; outcome -> score
+               (0 0)
+               (1 3)
+               (2 6)
+               (t 0))))))