dhruvsomani's blog

By dhruvsomani, history, 4 months ago, In English,

Hey, I could not understand the solution of a problem and I need some help.

Here's the problem I am talking about. BOI 2009, Candy Machine.

In this solution, I understood the O(n^2) algo with OWSP. Can you please explain what the O(n log n) solution (the code part) is doing.

Why is it sorting on basis of (t + p, t — p)? And what is the binary search on?

Please help. :)

Thanks.

 
 
 
 
  • Vote: I like it  
  • +5
  • Vote: I do not like it  

»
3 months ago, # |
  Vote: I like it 0 Vote: I do not like it

You do sweep line y=c-x with increasing c. If we maintain the set of wagons, you can see that each wagon can catch candies with y>=w+x. It is optimal to choose the one with wighest w.