Dijkstra's algorithm should not be O(n^2)

[lucky-bai]

While studying for the cs341 final, it occurred to me that my implementation of Dijkstra is bad and runs in quadratic time. It should be O(n log n) if we use priority queue like we're supposed to. Not super high priority to fix because performance is fast enough in most cases, but adding to to-do list.

Also iOS should be updated as well, of course.