QuadHeap instead of BinHeap in Dijkstra

[Peter Kovacs]

It is questionable whether Dijkstra should use QuadHeap instead of BinHeap by default.

In theory, a fourary heap is at least as efficient as a binary heap independently of the actual use case. I made some benchmark tests in which QuadHeap turned out to be typically faster than BinHeap, especially when many decrease() operations are performed. See the benchmark results here​. However, binary heap is the "standard" choice.

[Peter Kovacs]

In fact, this question does not seem to be important. I don't mind if it is closed. #381 seems to be much more interesting.