My Advents of Code

2015>9 - All in a Single Night

Description

Every year, Santa manages to deliver all of his presents in a single night.

This year, however, he has some new locations to visit; his elves have provided him the distances between every pair of locations. He can start and end at any two (different) locations he wants, but he must visit each location exactly once. What is the shortest distance he can travel to achieve this?

For example, given the following distances:

London to Dublin = 464
London to Belfast = 518
Dublin to Belfast = 141

The possible routes are therefore:

Dublin -> London -> Belfast = 982
London -> Dublin -> Belfast = 605
London -> Belfast -> Dublin = 659
Dublin -> Belfast -> London = 659
Belfast -> Dublin -> London = 605
Belfast -> London -> Dublin = 982

The shortest of these is London -> Dublin -> Belfast = 605, and so the answer is 605 in this example.

What is the distance of the shortest route?

--- Part Two ---

The next year, just to show off, Santa decides to take the route with the longest distance instead.

He can still start and end at any two (different) locations he wants, and he still must visit each location exactly once.

For example, given the distances above, the longest route would be 982 via (for example) Dublin -> London -> Belfast.

What is the distance of the longest route?

Notes

  • *** CHEAT SOLVE ***
  • This seems like a Traveling Salesman problem, but all the algorithms I've found assume returning home, so I'm not yet sure how to implement
  • Tried a couple different algorithms I found, including a plugin that solves a distance matrix (2d array of distances between all points), and while they got the test data correct, the real data failed
  • After many, many hours trying to figure this one out, I finally gave up and trawled Reddit solutions. Found one that worked, but now I need to figure out why.
  • Spent some time deconstructing the code, but still don't get this one. Big ol' ASTERISK on this.