1 files changed, 30 insertions, 0 deletions
diff --git a/day15/day15-1.js b/day15/day15-1.js
new file mode 100644
index 0000000..45a4ff1
--- /dev/null
+++ b/day15/day15-1.js
@@ -0,0 +1,30 @@
+const data = [0,3,6]
+
+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(2020)
+console.log(last)
+