POJ 1144

思路：求割点

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int v = 105;
int edge[v][v];
int bridge[v][v], cut[v];
int low[v], dfn[v], vis[v];
void cut_bridge(int cur, int father, int dep, int n){
    vis[cur] = 1;dfn[cur] = low[cur] = dep;
    int children = 0;
    for(int i = 0;i < n;i ++) if(edge[cur][i]){
        if(i != father && 1 == vis[i]){
            if(dfn[i] < low[cur]) low[cur] = dfn[i];
        }
        if(0 == vis[i]){
            cut_bridge(i, cur, dep+1, n);
            children ++;
            if(low[i] < low[cur]) low[cur] = low[i];
            if((father == -1 && children > 1) || (father != -1 && low[i] >= dfn[cur])) cut[cur] = 1;
        }
        if(low[i] > dfn[cur]) bridge[i][cur] = bridge[cur][i] = 1;
    }
    vis[cur] = 2;
}

int main(){
    int n, temp, u;
    /* freopen("in.c", "r", stdin); */
    while(~scanf("%d", &n) && n){
        memset(vis, 0, sizeof(vis));
        memset(dfn, 0, sizeof(dfn));
        memset(low, 0, sizeof(low));
        memset(cut, 0, sizeof(cut));
        memset(edge, 0, sizeof(edge));
        scanf("%d", &temp);
        while(temp){
            while(getchar() != '\n'){
                scanf("%d", &u);
                edge[u-1][temp-1] = edge[temp-1][u-1] = 1;
            }
            scanf("%d", &temp);
        }
        int ans = 0;
        cut_bridge(1, -1, 0, n);
        for(int i = 0;i < n;i ++ ){
            if(cut[i]) ans ++;
        }
        printf("%d\n", ans);
    }
    return 0;
}