Problem 67

In order to solve this problem, I tried to use the solution of problem 18, however that didn’t work… Therefore, I started by looking into some Haskell libraries and I came across the zipWith function. I used it before, however I didn’t remember it when I solved problem 18. The truth is that by using it together with the foldr1 function, it simplified the solution drastically. Here is my solution:

    import Examples

    total67 = head . foldr1 f
      where f x1 x2 = let l = zipWith max (init x2) (tail x2)
                      in zipWith (+) x1 l

The triangles were saved inside another module (Examples). In order to save the triangle used in this problem, I used a small python script to insert a list syntax into the text file:

    o = open("triangle.hs","a")
    i = open("triangle.txt")
    for line in open("triangle.txt"):
       line = line.replace(" ",",")
       line = line.strip()
       line = " [" + line + "],\n"
       o.write(line)
    o.close()

GHCi executes this function in (0.08 secs, 34504884 bytes).