CAPCITY - Capital City

There are N cities in Flatland connected with M unidirectional roads. The cities are numbered from 1 to N. The Flat Circle of Flatland (FCF) wants to set up a new capital city for his kingdom. For security reasons, the capital must be reachable from all other cities of Flatland. FCF needs the list of all candidate cities. You are the chief programmer at FACM (Flat Association for Computing Machinery) responsible for providing the list to FCF as soon as possible.


The first line of the input file contains two integers: 1 ≤ N ≤ 100,000 and 1 ≤ M ≤ 200,000. Each of the following M lines contains two integers 1 ≤ A, B ≤ N denoting a road from A to B.


The output file contains an integer denoting the number of candidate cities followed by the list of candidate cities in increasing order.


4 4
1 2
3 2
4 3
2 1

1 2

hide comments
kartikay singh: 2016-01-30 09:56:55

Nice problemo... :D

Deepak : 2016-01-25 19:28:53

weak test cases...was sure my solution will give WA..but got AC..copy paste BOTTOM.

Arjav: 2016-01-25 18:54:55

nice one ...... think reverse!!!

varun yadav: 2016-01-25 16:49:33

was afraid to submit,, but got AC in one go,, should be moved to tutorial :p

kejriwal: 2015-12-24 18:04:27

AC in one go.. :D !!

LEMONICE: 2015-10-22 21:08:24

Great question! Got to learn a lot!

Saket Sharma: 2015-07-03 07:55:01

it giving me runtime error :(
in test case 20. anyone please give me hint to solve pls.

likethis: 2015-06-16 04:34:27

nice problem

Dipti Singhal: 2015-05-31 09:57:58

Getting WA in 20th test case!

Potra Vlad: 2015-03-19 17:03:42

What's so special about 20th test case?

Added by:Narek Saribekyan
Time limit:1s-4s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Resource:Armenian TST 2010, Round 2