- reduce duplicate queue entries by not appending to the queue if a
point has a nonzero count. (if there's a count then it must have
already been queued.)
- use the correct data structure for a double-ended queue so pop(0) has
less work to do
- factor out the list of summits
of these three changes, only the last one has any noticable effect
on the run time. 🤷
magical
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