레이팅 미적용There are \(N\)
cities in one country that are connected with two-way air links. One crazy airline
president, Ronald Krump, often changes the flight schedule. More precisely, every day he
does the following:
●
chooses one of the cities,
●
introduces flights from that city towards all other cities where these flights do not
currently exist, and at the same time cancels all existing flights from that city
For instance, if from city 5 flights exist towards cities 1 and 2, but not towards cities 3 and 4,
after Krump’s change, there will exist flights from city 5 towards cities 3 and 4, but not
towards cities 1 and 2.
The citizens of this country are wondering if a day could come when the flight schedule will
be complete. In other words, when between each two different cities a (direct) flight will exist.
Write a programme that will, based on the current flight schedule, determine whether it is
possible to have a Complete Day
, or whether this will never happen, no matter what moves
Krump makes.
The first line of input contains the integer \(N\)
(\(2 \le N\)
≤ 1000), the number of cities. The cities
are labeled with numbers from 1 to \(N\)
.
The second line contains the integer \(M\)
(\(0 \le M\)
< N*(\(N-1\))/2
), the number of current flights.
Each of the following \(M\)
lines contains two different numbers, the labels of the cities that are
currently connected.
The first and only line of output must contain DA (Croatian for “yes”) or NE (Croatian for
“no”).
2
0
DA
3
2
1 2
2 3
NE
4
2
1 3
2 4
DA