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You've built an inflight entertainment system with on-demand movie streaming.

Users on longer flights like to start a second movie right when their first one ends, but they complain that the plane usually lands before they can see the ending. So you're building a feature for choosing two movies whose total runtimes will equal the exact flight length.

Write a function that takes an integer flightLength (in minutes) and an array of integers movieLengths (in minutes) and returns a boolean indicating whether there are two numbers in movieLengths whose sum equals flightLength.

When building your function:

  • Assume your users will watch exactly two movies
  • Don't make your users watch the same movie twice
  • Optimize for runtime over memory

We can do this in time, where n is the length of movieLengths.

Remember: your users shouldn't watch the same movie twice. Are you sure your function won’t give a false positive if the array has one element that is half flightLength?

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time, and space. Note while optimizing runtime we added a bit of space cost.

  1. What if we wanted the movie lengths to sum to something close to the flight length (say, within 20 minutes)?
  2. What if we wanted to fill the flight length as nicely as possible with any number of movies (not just 2)?
  3. What if we knew that movieLengths was sorted? Could we save some space and/or time?

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