From b4dcb59a8ace92d2a4343ad41a9230b727b1b850 Mon Sep 17 00:00:00 2001
From: j-james
Date: Tue, 12 Jan 2021 16:18:06 -0800
Subject: Day Fifteen

---
 2020/fifteen.nim       | 20 ++++++++++++++++++++
 2020/input/fifteen.txt |  1 +
 2 files changed, 21 insertions(+)
 create mode 100644 2020/fifteen.nim
 create mode 100644 2020/input/fifteen.txt

diff --git a/2020/fifteen.nim b/2020/fifteen.nim
new file mode 100644
index 0000000..0086054
--- /dev/null
+++ b/2020/fifteen.nim
@@ -0,0 +1,20 @@
+# Day Fifteen: Rambunctious Recitation
+import os, strutils, sequtils
+
+let input: string = paramStr(1)
+
+proc recite(nth: int): int =
+  var numbers: seq[int] = map(split(strip(readFile(input)), ","), parseInt)
+  var history: seq[int] = newSeqWith[int](nth, -1)
+  for i in 0 .. nth - 2:
+    let previous: int = numbers[i]
+    if i == len(numbers) - 1:
+      if history[previous] != -1:
+        numbers.add(i - history[previous])
+      else:
+        numbers.add(0)
+    history[previous] = i
+  return numbers[^1]
+
+echo recite(2020)
+echo recite(30000000)
diff --git a/2020/input/fifteen.txt b/2020/input/fifteen.txt
new file mode 100644
index 0000000..ef94aa4
--- /dev/null
+++ b/2020/input/fifteen.txt
@@ -0,0 +1 @@
+20,0,1,11,6,3
-- 
cgit v1.2.3-70-g09d2