391. Number of Airplanes in the Sky

391. Number of Airplanes in the Sky
Given an interval list which are flying and landing time of the flight. How many airplanes are on the sky at most?

Example
For interval list

[
  (1,10),
  (2,3),
  (5,8),
  (4,7)
]
Return 3

Notice
If landing and flying happens at the same time, we consider landing should happen at first.

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原文地址：https://www.cnblogs.com/lawrenceSeattle/p/10294086.html