poj1144

求割点

模板：

void dfs(int fa, int u)
{
    low[u] = dfn[u] = cnt++;
    for (int i = 0; i < n; i++)
        if (g[u][i] && i != fa)
        {
            if (dfn[i] == -1)
            {
                dfs(u, i);
                low[u] = min(low[i], low[u]);
                if (dfn[u] <= low[i])
                    is[u] = true;;
            }
            else
                low[u] = min(low[u], dfn[i]);
        }
}


call:
memset(dfn, -1, sizeof(dfn));
memset(is, 0, sizeof(is));
for (int i = 0; i < n; i++)
    if (dfn[i] == -1)
    {
        dfn[i] = cnt++;
        int x = 0;
        for (int j = 0; j < n; j++)
            if (g[i][j] && dfn[j] == -1)
            {
                dfs(i, j);
                x++;
            }
        if (x > 1)
            is[i] = true;
    }

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define maxn 105

bool g[maxn][maxn], is[maxn];
char st[maxn * maxn];
int dfn[maxn], low[maxn];
int cnt;
int ans;
int n;

void input()
{
    memset(g, 0, sizeof(g));
    int a, b;
    while (scanf("%d", &a), a)
    {
        a--;
        if (getchar() != ' ')
            continue;
        do
        {
            scanf("%d", &b);
            b--;
            g[a][b] = true;
            g[b][a] = true;
        } while (getchar() == ' ');
    }
}

void dfs(int fa, int u)
{
    low[u] = dfn[u] = cnt++;
    for (int i = 0; i < n; i++)
        if (g[u][i] && i != fa)
        {
            if (dfn[i] == -1)
            {
                dfs(u, i);
                low[u] = min(low[i], low[u]);
                if (dfn[u] <= low[i])
                    is[u] = true;;
            }
            else
                low[u] = min(low[u], dfn[i]);
        }
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%d", &n), n)
    {
        getchar();
        cnt = 0;
        ans = 0;
        input();
        memset(dfn, -1, sizeof(dfn));
        memset(is, 0, sizeof(is));
        for (int i = 0; i < n; i++)
            if (dfn[i] == -1)
            {
                dfn[i] = cnt++;
                int x = 0;
                for (int j = 0; j < n; j++)
                    if (g[i][j] && dfn[j] == -1)
                    {
                        dfs(i, j);
                        x++;
                    }
                if (x > 1)
                    is[i] = true;
            }
        for (int i = 0; i < n; i++)
            if (is[i])
                ans++;
        printf("%d\n", ans);
    }
    return 0;
}