perf(fringe): stop scanning the whole fringe on every relaxed edge - #810
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Reaching a node through a cheaper path has to move it back to the front of the current list. `remove` finds it by walking `later` and then `now` from one end, comparing indices, so every relaxed edge costs a pass over the fringe. The fringe is large for exactly the searches that matter, which makes the inner loop quadratic in its size. Leave the stale entries where they are instead. Each queue entry carries the value `stamps[node]` held when it was queued, and relaxing a node bumps its stamp, so the older entries are recognised and skipped when they come up. The node is pushed to the front as before, so it is still reached first, and the work per edge drops to a push. Nothing else about the search changes: the same nodes are expanded under the same limits, and paths are checked against Bellman-Ford over 300 random graphs. About 42% off a 200x200 weighted grid. The gap widens with the size of the fringe, so larger searches gain more.
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Closes #806.
Leaves stale queue entries in place instead of scanning for them. Each entry carries the value
stamps[node]held when it was queued; relaxing a node bumps its stamp, so older entries are recognised and skipped when they surface. The node is still pushed to the front, so it is still reached first, and the work per relaxed edge drops to a push.removegoes away with it.Checking
The search itself is unchanged: the same nodes are expanded under the same limits, and the same path comes out. Verified against Bellman-Ford over 300 random graphs, and the existing
fringetests, including the GPS and r299 ones, are untouched.About 42% off a 200x200 weighted grid, measured against this branch's parent. The gap widens with the size of the fringe.
All timings measured on Windows 11, Intel Core Ultra 7 265K, 64 GB RAM.