Active Couriers Timeline

You are given couriers, where couriers[i] = [start, end] represents the working interval of the ith courier. start is inclusive and end is exclusive. Intervals may overlap. Return a list of timeline segments [segmentStart, segmentEnd, activeCount] such that:

• activeCount is the number of couriers working throughout the entire segment.
• You only create a new segment when the number of active couriers changes.
• Only segments with activeCount > 0 should appear in the output. If multiple couriers start or end at the same time, treat all changes at that timestamp together before moving to the next segment.

From 1 to 3, one courier is active. From 3 to 5, both are active. From 5 to 7, only the second courier remains.

Because intervals are [start, end), the courier ending at 3 is not active at time 3, while the two couriers starting at 3 are.