Hot Air Balloon Booking

Problem

Given a list of flight intervals flights where flights[i] = [start_i, end_i] represents the start and end times of a flight, determine the minimum number of hot air balloons required to schedule all the flights so that no two flights on the same balloon overlap in time.

Examples

minHotAirBalloons([[5,9],[1,3]])
// returns 1
// Balloon 1: Flight from 1 to 3 and flight from 5 to 9

minHotAirBalloons([[5,9],[1,3],[2,6]])
// returns 2
/* Balloon 1: Flight from 1 to 3
Balloon 2: Flight from 2 to 6
(since balloon1 is occupied)
Balloon 1: Flight from 5 to 9
(since the 1st flight in balloon1 is over)
*/