【lightoj-1063】Ant Hills(求割点)

求割点模板题

#include <bits/stdc++.h>
using namespace std;
const int N = 10004;
int dfn[N], low[N];
bool ok[N];
vector<int>V[N];
int n, num, root;
void dfs(int s, int f)
{
    low[s] = dfn[s] = ++num;
    int child = 0;
    for(unsigned int i = 0; i < V[s].size(); i++)
    {
        int v = V[s][i];
        if(!dfn[v])
        {
            child++;
            dfs(v, s);
            low[s] = min(low[s], low[v]);//更新s节点能访问到最早的时间戳
            if(low[v] >= dfn[s] && s != root)
                ok[s] = 1;
            if(s == root && child >= 2) ok[s] = 1;
        }
        else if(v != f) low[s] = min(low[s], dfn[v]);
    }
}
int main()
{
    int t, n, cas = 0, m, a, b;
    //freopen("1.txt", "w", stdout);
    cin>>t;
    while(t--)
    {
        memset(dfn, 0, sizeof dfn);
        memset(low, 0, sizeof low);
        memset(ok, 0, sizeof ok);
        scanf("%d%d", &n, &m);
        for(int i = 0 ; i <= n; i++) V[i].clear();
        num = 0;
        for(int i = 1; i <= m; i++)
        {
            scanf("%d%d", &a, &b);
            V[a].push_back(b);
            V[b].push_back(a);
        }
        for(int i = 1; i <= n; i++)//图不一定连通
        {
            if(!dfn[i])
            {
                root = i;
                dfs(i, i);
            }
        }
        int ans = 0;
        for(int i = 1; i <= n; i++)
            if(ok[i]) ans++;
        printf("Case %d: %d\n", ++cas, ans);
    }
    return 0;
}