Tomorrow got to busy. I put it up tonight.

…mrt

Josh

Tomorrow night I’ll try to post my VBA implementation of Doug’s approach. Please feel free to answer with your implementation. We’ll try to get all this Problem 83 stuff in a Problem 83 thread

Note Dick’s advice about posting code inside [ V B ] tags, and be watchful for angle bracket pairs inside the VB tags. WordPress treats those pairs as html and hides (throws away) anything in there. Has the virtue of shortening your code I use LT, GT, LTE, GTE and != for the angle brackets.

Thanks for the steer on Graeme. Another author to look for is petrw1. He writes in BASIC. If you DIM his variables and change his PRINT to debug.print, it’ll usually run. He’s no good at telling you what his variables do, though.

…mrt

My first attempt solved the problem in about 3s, but I noticed that about 98% of the time was finding the node with the current lowest cost, as in step 1. Each time through, I was looping through all 6400 points, looking for the lowest value. Obviously, an extreme waste of time. After some searching, I decided to learn something new and use a priority queue in the form of a binary heap to always keep track of the node with the lowest cost. I had a heck of a time fiddling with array indices, but eventually the answer came out in 0.1s. I’d be happy to post the code if anyone is interested. I used basically the same code (without the priority queue) for 81 & 82, only changing which nodes are considered as neighbors.

If you manage to solve a problem and you’re looking at the forum posts for insight, then I recommend that you look for postings by a user named GraemeMcRae. He does the problems with spreadsheet / VBA. His solutions are concise, highly readable, and thoroughly explained. He also appears to have a strong math background and does a good job with explanations. I’ve learned quite a bit from him.

-Josh

In the spirit of Project Euler, we try not to post the answers, particularly the right ones . So, Euler forgive us…

If you join Project Euler (http://projecteuler.net/index.php), when you then further click on a problem, there is a submit button. Submitting your answer will either come back with a nice apology that “We’re sorry, but your answer appears to be incorrect…” or a check mark and admission into the often-locked discussion group with those that have also solved the problem. Occasionally, there is also a pdf file that provides more insight. Most solutions offered on the inside are written in obfuscated code, usually Python, and often by high-schoolers. But there are a few gems among the pebbles. An author named “rayfil” does the problems in assembly, and while there are some BASIC authors, not many, if any at all, post VBA. That’s what led me to ask Dick if I could post here.

Doug Jenkins beat you to it and did exactly your spreadsheet solution in the 123 thread. That’s were I first brought up my #83 ineptitude.

The number of apologies I’ve received greatly exceeds the number of checkmarks…

…mrt

(Edited by Michael to conceal the answer)

(Edited by Michael to conceal the answer)

Yep, never said it was hard. Except for the order of cells in the MIN() that was exactly my approach, down to having the answer is A101. Must have been looking over my shoulder… Nicely, the MIN() ignores empty cells beyond the boundaries. In VBA I got out-of-range errors. That necessitated the early rollups of the right and bottom.

Now, #82 and #83 (using the same matrix) are tougher. See Doug’s iterative spreadsheet solution in the 123 thread for #83.

…mrt

LOL! Yes, Euler 81 is trivial to solve in Excel. Suppose the matrix is in A1:CB80.

In CB180 enter =CB80+MIN(CB181,CC180). Copy it to A180:CA180. Copy A180:CB180 to rows 101:179. A101 will have the desired answer.