Problem 18
http://projecteuler.net/index.php?section=problems&id=18
上からたどった経路の数字を全て足したときの最大値は? (問題は15段)
3 7 5 2 4 6
これだと14が最大値 (3→7→4 or 3→5→6)
import List main = print $ maximum $ foldl1 f triangle f xs ys@(_:ys') = zipWith max rs0 rs1 where rs0 = zipWith (+) xs ys ++ [0] rs1 = 0 : zipWith (+) xs ys' triangle = [ [75], [95, 64], [17, 47, 82], [18, 35, 87, 10], [20, 04, 82, 47, 65], [19, 01, 23, 75, 03, 34], [88, 02, 77, 73, 07, 63, 67], [99, 65, 04, 28, 06, 16, 70, 92], [41, 41, 26, 56, 83, 40, 80, 70, 33], [41, 48, 72, 33, 47, 32, 37, 16, 94, 29], [53, 71, 44, 65, 25, 43, 91, 52, 97, 51, 14], [70, 11, 33, 28, 77, 73, 17, 78, 39, 68, 17, 57], [91, 71, 52, 38, 17, 14, 91, 43, 58, 50, 27, 29, 48], [63, 66, 04, 68, 89, 53, 67, 30, 73, 16, 69, 87, 40, 31], [04, 62, 98, 27, 23, 09, 70, 98, 73, 93, 38, 53, 60, 04, 23] ]
リストの最後に要素を足すという処理を書きたくないのだが。