PairingHeap

PairingHeap is a pure Ruby priority queue implementation using a pairing
heap as the underlying data structure.  While a pairing heap is
asymptotically less efficient than the Fibonacci heap, it is usually faster
in practice.  This makes it a popular choice for Prim's MST or Dijkstra's
algorithm implementations.

PairingHeap is currently being used as the priority queue data structure in
RGL (https://github.com/monora/rgl/).

Also implementation without priority change support is provided
(SimplePairingHeap), while the asymptotical complexity of the methods stay
the same, bookkeeping of elements is not needed making, the constant
smaller.