How far a traversal got before it was cut short, so a caller can judge a truncated slice instead of having to drop it: a frontier of 0 means the queue drained after all, and a small frontier next to a large visited says little is missing.
frontier
0
visited
Readonly
entries still queued when it stopped
queue entries the traversal expanded
How far a traversal got before it was cut short, so a caller can judge a truncated slice instead of having to drop it: a
frontierof0means the queue drained after all, and a smallfrontiernext to a largevisitedsays little is missing.