Day 17 done

[advent-of-code-17.git] / src / advent17 / advent17leaky.hs

diff --git a/src/advent17/advent17leaky.hs b/src/advent17/advent17leaky.hs
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+{-# LANGUAGE NegativeLiterals #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE NegativeLiterals #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE BangPatterns #-}
+
+import Prelude hiding ((++))
+import Data.Vector.Unboxed ((!), (++))
+import qualified Data.Vector.Unboxed as V
+import qualified Data.List as L
+
+type RingBuffer = V.Vector Int
+
+initialStepSize :: Int
+initialStepSize = 366
+
+initialRingBuffer :: RingBuffer
+initialRingBuffer = V.singleton 0
+
+
+main :: IO ()
+main = do 
+        print $ part1 initialStepSize 2017
+        print $ part2 initialStepSize 50000000
+
+
+part1 n k = (!1) $! last $! take k $! L.unfoldr ringBufferUnfolder (1, n, initialRingBuffer)
+
+
+part2 n k = finalBuffer!targetLoc
+    where finalBuffer = last $! take k $! L.unfoldr ringBufferUnfolder (1, n, initialRingBuffer)
+          zeroLoc = V.head $ V.elemIndices 0 finalBuffer
+          targetLoc = (zeroLoc + 1) `rem` (V.length finalBuffer)
+
+
+updateRingBuffer nextValue stepSize buffer = (buffer', stepSize)
+    where !nextPos = (stepSize + 1) `rem` V.length buffer
+          (!start, !end) = V.splitAt nextPos buffer
+          !buffer' = V.cons nextValue $ end ++ start
+
+ringBufferUnfolder :: (Int, Int, RingBuffer) -> Maybe (RingBuffer, (Int, Int, RingBuffer))
+ringBufferUnfolder (nextValue, stepSize, buffer) = Just (buffer', (nextValue + 1, stepSize', buffer'))
+    where (!buffer', !stepSize') = updateRingBuffer nextValue stepSize buffer
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