Description
Blackouts and Dark Nights (also known as ACM++) is a company that provides electricity. The company owns several power plants, each of them supplying a small area that surrounds it. This organization brings a lot of problems - it often happens that there is not enough power in one area, while there is a large surplus in the rest of the country.
ACM++ has therefore decided to connect the networks of some
of the plants together. At least in the first stage, there is no need to
connect all plants to a single network, but on the other hand it may
pay up to create redundant connections on critical places - i.e. the
network may contain cycles. Various plans for the connections were
proposed, and the complicated phase of evaluation of them has begun.
One of the criteria that has to be taken into account is the
reliability of the created network. To evaluate it, we assume that the
worst event that can happen is a malfunction in one of the joining
points at the power plants, which might cause the network to split into
several parts. While each of these parts could still work, each of them
would have to cope with the problems, so it is essential to minimize the
number of parts into which the network will split due to removal of one
of the joining points.
Your task is to write a software that would help evaluating
this risk. Your program is given a description of the network, and it
should determine the maximum number of non-connected parts from that the
network may consist after removal of one of the joining points (not
counting the removed joining point itself).
Input
The input consists of several instances.
The first line of each instance contains two integers 1 <=
P <= 10 000 and C >= 0 separated by a single space. P is the
number of power plants. The power plants have assigned integers between 0
and P - 1. C is the number of connections. The following C lines of the
instance describe the connections. Each of the lines contains two
integers 0 <= p1, p2 < P separated by a single space, meaning that
plants with numbers p1 and p2 are connected. Each connection is
described exactly once and there is at most one connection between every
two plants.
The instances follow each other immediately, without any separator. The input is terminated by a line containing two zeros.
Output
The output consists of several lines. The i-th line of the output
corresponds to the i-th input instance. Each line of the output
consists of a single integer C. C is the maximum number of the connected
parts of the network that can be obtained by removing one of the
joining points at power plants in the instance.
Sample Input
3 3
0 1
0 2
2 1
4 2
0 1
2 3
3 1
1 0
0 0
Sample Output
1
2
2
分析：一道无向图求割点的模板题，今天初学，是看着LRJ的书写的，一直调不对，看了看网上的题解，有一篇的代码很简洁，
对LRJ的写法做了调整，主要是省略了child和iscut，用一个cut数组代替，这样的好处是避免dfs中变量太多影响理解。
cut的含义是：删除这个结点后被断开的儿子结点个数，也就是删除这个结点增加的连通分量个数。
这里只要注意根结点没有父节点，因此根结点的cut要-1。最后统计的是所有节点cut的最大值。由于每个节点都有cut，就不用像LRJ书上那样，
每次判断iscut了。确实方便不少。
注意：ans的初始化应该是连通分量个数-1，我一开始初始化为连通分量个数，一直WA，查了半天。。
代码
Inference
1.focus_best的博客
