1 files changed, 45 insertions, 0 deletions
diff --git a/2022/Day2/part-one.cl b/2022/Day2/part-one.cl
new file mode 100644
index 0000000..e93cae8
--- /dev/null
+++ b/2022/Day2/part-one.cl
@@ -0,0 +1,45 @@
+(defvar *prog-input*)
+
+(let ((ui (read-line)))
+  (if (equal ui "")
+    (setq *prog-input* *standard-input*)
+    (setq *prog-input* (open ui))))
+
+(let
+  ((cal (read-line *prog-input* NIL)) (total-score 0)
+   (your-rps '(#\0 #\X #\Y #\Z)) (enemy-rps '(#\0 #\A #\B #\C))
+   (cy-rps 0) (ce-rps 0))
+
+  (loop until (or (equal cal "end") (not cal)) do
+        ;; Rock is 1, paper is 2, scissors is 3
+        (setq ce-rps (position (char cal 0) enemy-rps))
+        (setq cy-rps (position (char cal 2) your-rps))
+
+        ;; We want, when we lose to add 3 * 0, when we draw to add 3 * 1 and when we win to add 3 * 2
+        ;; To get numbers 0, 1, and 2, we'll use `3 mod N`
+        ;; Writing down all possible combinations
+        ;; (from left to right, columns are "Your choice", "Enemy choice", "Result"):
+        ;; 1 1 | 1 = 3 % 1 (Draw)
+        ;; 1 2 | 0 = 3 % 3 (Lose)
+        ;; 1 3 | 2 = 3 % 2 (Win)
+        ;; ----+-----------------
+        ;; 2 1 | 2 = 3 % 2 (Win)
+        ;; 2 2 | 1 = 3 % 1 (Draw)
+        ;; 2 3 | 0 = 3 % 3 (Lose)
+        ;; ----+-----------------
+        ;; 3 1 | 0 = 3 % 3 (Lose)
+        ;; 3 2 | 2 = 3 % 2 (Win)
+        ;; 3 3 | 1 = 3 % 1 (Draw)
+        ;; We notice, that N (in "3 % N") is a rotation of the numbers 3, 2, 1, where if your choice
+        ;; is 3, we don't rotate them, if it's 2 we rotate by one (backwards) and so on.
+        ;; We can get 3, 2, 1 from the enemie's 1, 2, 3 by subtracting them from 4. Then we can use
+        ;; your choice to do the "rotation" (since we're doing mod, 3 % 3 = 3 % 6).
+        (setq total-score (+ total-score (* 3 (mod (+ (- 4 ce-rps) cy-rps) 3)) cy-rps))
+
+        (setq cal (read-line *prog-input* NIL)))
+
+  (print total-score))
+
+(if (not (eq *prog-input* *standard-input*))
+  (close *prog-input*))
+