PyPE solution to PE problem 67

    ProjectEuler.net problem 67
    ===========================

    By starting at the top of the triangle below and moving to adjacent numbers
    on the row below, the maximum total from top to bottom is 23.

    3
    7 5
    2 4 6
    8 5 9 3

    That is, 3 + 7 + 4 + 9 = 23.

    Find the maximum total from top to bottom in triangle.txt (right click and
    'Save Link/Target As...'), a 15K text file containing a triangle with one-
    hundred rows.

    NOTE: This is a much more difficult version of Problem 18. It is not
    possible to try every route to solve this problem, as there are 2^99
    altogether! If you could check one trillion (10^12) routes every second it
    would take over twenty billion years to check them all. There is an
    efficient algorithm to solve it. ;o)

    Solution
    --------

    Note that an efficient algorithm for solving this has already been developed
    for problem 18. Please refer to PyPE.solutions.pype_018 for a description of
    the solution algorithm.

    Answer
    ------

    7273