Around the World (#138)
There is an airport on an island with an unlimited number of identical airplanes. When fully fueled, an airplane can fly exactly half the distance around the world along a great circle. Airplanes can refuel each other perfectly in flight without loss of speed, fuel, or time. What is the minimum number of airplanes needed on the island for one airplane to make a round-the-world trip, given that all airplanes must return safely to the island?
Note: Assume that refueling happens instantaneously in any volume. Fuel is consumed evenly. Fuel supplies on the island are unlimited, but the island is the only source of fuel.
Complexity: 5/10