[doctor_phil]

Why does the fix need to remember all the nodes we have visited? Can't we just keep track of what span we are in? That way we just need to keep track of 2 nodes.

In the graphic from the example we would keep track like this:

  low: - high -
  low: 11 high: -
  low: 23 high: -
  low: 23 high: 26
  Error: now we see item 13, but that is not inside our span!