C# – CodeForces – Two TVs

Having two TVs is great. Or it used to be in the 90s. Anyhow, the latest problem in CodeForces that I have resolved was concerning a guy with a schedule of TV shows, which he was planning to watch on his two TVs.

cs

Polycarp is a great fan of television.

He wrote down all the TV programs he is interested in for today. His list contains n shows, i-th of them starts at moment li and ends at moment ri.

Polycarp owns two TVs. He can watch two different shows simultaneously with two TVs but he can only watch one show at any given moment on a single TV. If one show ends at the same moment some other show starts then you can’t watch them on a single TV.

Polycarp wants to check out all n shows. Are two TVs enough to do so?

Input

The first line contains one integer n (1 ≤ n ≤ 2·105) — the number of shows.

Each of the next n lines contains two integers li and ri (0 ≤ li < ri ≤ 109) — starting and ending time of i-th show.

Output

If Polycarp is able to check out all the shows using only two TVs then print “YES” (without quotes). Otherwise, print “NO” (without quotes).


The solution was advised to be made with a single sorted list, containing both the start and the end of the shows, with a flag indicating whether it is a start or an end. However, I liked the idea that there should be a way to solve the problem with two lists, one for starts and one for the ends of the show. And as far as I have two TVs in the problem, I am allowed to have maximum two positions from the end list, which are not before the positions in the start list. To maintain these positions, I have used a Queue (as far as I have not used it in quite a while) and at the end the solution was successful! 🙂

Cheers!

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