Time limit 2000/4000/4000/4000 ms. Memory limit 65000/65000/65000/65000 Kb.
Question by Osman Ay.
Traffic
Question:
The heavy traffic is one of the major problems of
big cities. The city municipalities try to find
different solutions for this problem. The solution
of the Tirana municipality is to make all the
roads in the city only in one direction. So that,
no two cars will block a narrow road. The only
issue of this solution is that if it is possible
to reach from any point of the city to any other
point after the transformation. Make a program
that reads the current undirected road connections
of the city and determines if it is possible to
convert all the roads to directed roads and still
possible to travel between any two places.
Input specification
The first line of the test case contains
two integers C (1 < C ≤ 30000)
and R (1 ≤ R ≤ 100000) where C is the number of
the road conjunctions and R is the number of
the roads in the city. There are no parallel
roads and no road connects a junction to itself.
Each of the following R lines determines a road
with two integers. Those integers represent
numbers of two conjunctions connected with the
road. The conjunctions are numbered from 1 to
C.
Output specification
The output contains a single word "YES" or "NO".
Sample Input I
4 5
1 2
4 3
2 4
4 1
2 3
|
Sample Input II
3 3
1 3
2 1
3 1
|
Sample Output I
YES
|
Sample Output II
NO
|
Для отправки решений необходимо выполнить вход.
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