题目链接
Description 问题描述
In order to get from one of the F (1 <= F <= 5,000) grazing fields (which are numbered 1..F) to another field, Bessie and the rest of the herd are forced to cross near the Tree of Rotten Apples. The cows are now tired of often being forced to take a particular path and want to build some new paths so that they will always have a choice of at least two separate routes between any pair of fields. They currently have at least one route between each pair of fields and want to have at least two. Of course, they can only travel on Official Paths when they move from one field to another.
Given a description of the current set of R (F1 <= R <= 10,000) paths that each connect exactly two different fields, determine the minimum number of new paths (each of which connects exactly two fields) that must be built so that there are at least two separate routes between any pair of fields. Routes are considered separate if they use none of the same paths, even if they visit the same intermediate field along the way.
There might already be more than one paths between the same pair of fields, and you may also build a new path that connects the same fields as some other path.
Input 输入
Line 1: Two spaceseparated integers: F and R
Lines 2..R+1: Each line contains two spaceseparated integers which are the fields at the endpoints of some path.
Output 输出
Line 1: A single integer that is the number of new paths that must be built.
样例输入
7 7
1 2
2 3
3 4
2 5
4 5
5 6
5 7
样例输出
2
思路
题意简述：求一个无向连通图中还需加入多少条边能构成一个边双连通分量。
不太好想。假设我们把桥留下来，然后对每个双联通分量进行缩点，因为是连通图，所以就能得到一棵树。
然后对这个树进行加边操作，可以发现一个结论：需要互通的点一定构成一个环。
然后画图不严谨证明得到最后答案就是叶子节点个数除以二然后向上取整。
代码
1 
