2647: Strongly Connected City 2
Time Limit: 2 Sec Memory Limit: 256 MBSubmit: 0 Solved: 0
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Description
Imagine a city with n junctions and m streets. Junctions are numbered from 1 to n.
In order to increase the traffic flow, mayor of the city has decided to make each street one-way. This means in the street between junctions u and v, the traffic moves only from u to v or only from v to u.
The problem is to direct the traffic flow of streets in a way that maximizes the number of pairs (u,v) where 1≤u,v≤n and it is possible to reach junction v from u by passing the streets in their specified direction. Your task is to find out maximal possible number of such pairs.
The first line of input contains integers n and m, (
), denoting the number of junctions and streets of the city.
Each of the following m lines contains two integers u and v, (u≠v), denoting endpoints of a street in the city.
Between every two junctions there will be at most one street. It is guaranteed that before mayor decision (when all streets were two-way) it was possible to reach each junction from any other junction.
Print the maximal number of pairs (u,v) such that that it is possible to reach junction v from u after directing the streets.
5 4
1 2
1 3
1 4
1 5
13
4 5
1 2
2 3
3 4
4 1
1 3
16
2 1
1 2
3
6 7
1 2
2 3
1 3
1 4
4 5
5 6
6 4
27
In the first sample, if the mayor makes first and second streets one-way towards the junction 1 and third and fourth streets in opposite direction, there would be 13 pairs of reachable junctions: {(1,1),(2,2),(3,3),(4,4),(5,5),(2,1),(3,1),(1,4),(1,5),(2,4),(2,5),(3,4),(3,5)}