From 6eb86da5efc99e63c58f1fc9a1f7e3706dd6a2dc Mon Sep 17 00:00:00 2001
From: Piotr Russ <mail@pruss.it>
Date: Tue, 15 Dec 2020 20:20:21 +0100
Subject: day15

---
 day15/day15-2.js | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 day15/day15-2.js

(limited to 'day15/day15-2.js')

diff --git a/day15/day15-2.js b/day15/day15-2.js
new file mode 100644
index 0000000..11b137c
--- /dev/null
+++ b/day15/day15-2.js
@@ -0,0 +1,30 @@
+const data = [0,13,1,16,6,17]
+
+const numbers = {}
+let last, prev1, prev2
+
+const game = (turns) => {
+  for (let i=1; i <= turns; i++) {
+    if (i <= data.length) {
+      numbers[data[i-1]] = [i, 0]
+      last = data[i-1]
+    } else {
+      [prev1, prev2] = numbers[last]
+      if (!prev2) {
+        last = 0
+        numbers[0] = [i, numbers[0][0]]
+      } else {
+        last = prev1 - prev2
+        if (numbers[last]) {
+          numbers[last] = [i, numbers[last][0]]
+        } else {
+          numbers[last] = [i, 0]
+        }
+      }
+    }
+  }
+}
+
+game(30000000)
+console.log(last)
+
-- 
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