POJ1144(求割点数目)

题目链接：https://vjudge.net/problem/POJ-1144

题意：给出N个点，然后下面若干行，某一行第一个数位u，之后若干个数为v，表示u,v有一条双向边。注意下输入。

题解：裸的Tarjan算法求割点数目。

#include 
#include 
#include 
#include 
#include 

using namespace std;


const int N = 107;

int low[N];
int dfn[N];
vectorG[N];
setS;
int index;
int root;


void Tarjan(int u, int fa)
{
    dfn[u] = low[u] = ++ index;
    int n = G[u].size();
    int son = 0;
    for(int i = 0;i < n;i ++) {
        int v = G[u][i];
        if(v == fa) continue;
        if(!dfn[v]) {
            son ++;
            Tarjan(v, u);
            low[u] = min(low[u], low[v]);
            if(root == u && son > 1 || root != u && low[v] >= dfn[u]) S.insert(u);
        } else {
            low[u] = min(low[u], dfn[v]);
        }
    }
}

int main()
{
    int n;
    while(scanf("%d", &n) && n) {
        int u;
        S.clear();
        for(int i = 1;i <= n;i ++) {
            dfn[i] = low[i] = 0;
            G[i].clear();
        }
        while(scanf("%d",&u) && u) {
            while((getchar()) != '\n') {
                int v;
                scanf("%d",&v);
                G[u].push_back(v);
                G[v].push_back(u);
            }
        }
        for(int i = 1;i <= n;i ++) {
            if(!dfn[i]) {
                index = 0;
                root = i;
                Tarjan(i, -1);
            }
        }
        printf("%d\n", (int)S.size());
    }
    return 0;
}