Question 18

src/projectEuler/question18.hs

@@ -0,0 +1,50 @@
+import           Debug.Trace (trace)
+small :: [[Integer]]
+small = [
+         [3],
+        [7,4],
+       [2,4,6],
+    [1000,5,9,3]
+  ]
+
+triangle :: [[Integer]]
+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]
+  ]
+
+maxPath t i j = (t !! i !! j) +
+  (if i + 1 < length t
+    then max (maxPath t (i + 1) j) (maxPath t (i + 1) (j + 1))
+    else 0)
+
+-- This max path doesn't consider the entire path,
+-- it only considers the two numbers directly below the index
+newMaxPath t i j = (t !! i !! j) +
+  (if i + 1 < length t
+    then newMaxPath t i' j'
+    else 0)
+  where
+    a = t !! i' !! j
+    b = t !! i' !! (j+1)
+    i' = i+1
+    j' = trace (show a) $ if a > b then j else j+1
+
+main :: IO ()
+main = print ans
+
+ans :: Integer
+ans = maxPath small 0 0

src/projectEuler/question4.hs

@@ -17,9 +17,9 @@ threeDigitProducts =  [ n*m | n <- [100..999], m <- [n..999] ]
 isPalindrome :: Integer -> Bool
 isPalindrome n = all (== True) $ zipWith (==) half half'
   where
-    (half, half'') = splitAt h n'
+    (half, half'') = splitAt l n'
     half' = reverse half''
-    h     = length n' `div` 2
+    l     = length n' `div` 2
     n'    = show n
     -- n' = trace (show n) $ show n