277. How Many Platforms
n trains arrive and depart at a station. Print the smallest number of
platforms needed so that no train ever waits.
A train occupies a platform from its arrival to its departure inclusive, so a train arriving at the exact moment another departs still needs its own platform.
The trains are given as two separate lists, and which arrival belongs to which departure does not matter. Sort each list independently and sweep: every arrival takes a platform, every departure frees one, and the answer is the largest number in use at any moment.
Constraints - `1 ≤ n ≤ 200000` - `0 ≤ arrival ≤ departure ≤ 1000000000`
Input
The first line contains an integer n.
The second line contains n arrival times.
The third line contains n departure times.
Output
Print one integer, the minimum number of platforms required.
Hints
Four rungs, in order. The last two open once you have submitted an attempt. A wrong one counts.