Arrows to burst balloons

Sort the balloons by where they end. The balloon that ends first needs an arrow somewhere inside it, and the best place is its very end: as far right as possible, so the same arrow also bursts every later balloon that has started by then. The first balloon that starts after the arrow needs a new one, again at its own end.

Each bar is a balloon on the x-axis, numbered by its index as on the slides, one lane per balloon in sorted order. A vertical line is an arrow; green balloons are burst by the latest arrow, grey ones by an earlier one.