The problem is not hard to solve once I realized that this is a standard problem for Dijkstra's algorithm. I used priority_queue in STL to solve this problem and succeeded. Everything looks great and I immediately started working on the next problem.
But I did not think it over. I read the related sections about the Dijkstra in CLRS.
One paragraph is focused on a function called decreaseKey. The weird thing is that there is no such functionality in STL and CLRS has no code snippet for it. So I just ignored it!
My experience with later-on project euler problems was awful when I can recognize that it is a Dijkstra problem, but with STL, my code ran extremely slow and required huge amount of memory! The root cause is simply that I do not have a function to fulfill the functionality of decreaseKey!
I reviewed this problem for one time two years ago, but I did not review the problem carefully and missed another learning opportunity!
The projecteuler+ on this problem also requires an efficient implementation of Dijkstra.
Learning is of top priority and the number of problem solved is not that important!
