Find minimum number of time points that cross out all intervals
Hint: 


   Try some more greedy algorithms; keep trying, and don't give up yet.  You might try solving some small examples by hand, to get some intuition for what is going on, and see what strategies you end up developing.  The way to look for a greedy algorithm is to try all greedy strategies you can think of -- it's not enough to just try one particular strategy and if that doesn't work give up on the entire paradigm of greedy algorithms.


This looks like a nice learning exercise, so keep at it.  You can do it.  (We're glad to help you understand concepts but just solving this exercise for you probably won't help with that.)