POJ2117割点连通分量

Posted 2021-08-24 hesorchen

题目

Electricity

答案为 连通分量数量+ MAX（tot-isroot）

代码

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <vector>
#include <stack>
#include <map>
using namespace std;

const int N = 100005;
vector<int> edge[N];
int dfn[N], low[N], ct, res;
void tarjan(int u, bool isroot)
{
    dfn[u] = low[u] = ++ct;
    int tot = 0; //删除该点后的连通分量数量即为tot-isroot
    for (int i = 0; i < edge[u].size(); i++)
    {
        int v = edge[u][i];
        if (!dfn[v])
        {
            tarjan(v, 0);
            low[u] = min(low[u], low[v]);
            tot += low[v] >= dfn[u];
        }
        else
            low[u] = min(low[u], dfn[v]);
    }
    res = max(res, tot - isroot);
}

int main()
{
    int n, m;
    while (cin >> n >> m)
    {
        if (n == 0 && m == 0)
            return 0;
        for (int i = 0; i <= n; i++)
            edge[i].clear();
        memset(dfn, 0, sizeof dfn);
        memset(low, 0, sizeof low);
        ct = 0;
        for (int i = 1; i <= m; i++)
        {
            int u, v;
            cin >> u >> v;
            ++u, ++v;
            edge[u].push_back(v);
            edge[v].push_back(u);
        }
        int ans = 0, maxx = 0;
        for (int i = 1; i <= n; i++)
        {
            if (!dfn[i])
            {
                ans++;
                res = 0;
                tarjan(i, 1);
                maxx = max(maxx, res);
            }
        }
        ans += maxx;
        if (ans == n)
            ans--;
        cout << ans << endl;
    }
    return 0;
}