The guidelines for Project Euler say that
Each problem has been designed according to a “one-minute rule”, which means that although it may take several hours to design a successful algorithm with more difficult problems, an efficient implementation will allow a solution to be obtained on a modestly powered computer in less than one minute.
which makes me think that my solution to problem 15,
Starting in the top left corner of a 2
2 grid, there are 6 routes (without backtracking) to the bottom right corner.
How many routes are there through a 20
which has been running since Wednesday, is less than optimal (makes me think I don’t quite deserve the 9% genius rating). I am sure it is going to find the right answer and I calculated that it would take three days. When it is done, I’ll try to get it down to a minute. That’s part of the fun.
Since #15 is taking such a long time, I skipped to some later problems. #18 was fun:
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 3That is, 3 + 7 + 4 + 9 = 23.
Find the maximum total from top to bottom of the triangle below
My recursive solution below the fold (no peeking until you have solved it).