Day Fifteen

2 files changed, 21 insertions, 0 deletions

diff --git a/2020/fifteen.nim b/2020/fifteen.nim
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+# 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
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+++ b/2020/input/fifteen.txt
@@ -0,0 +1 @@
+20,0,1,11,6,3