TOJ 2018 SPF / 割点&&双联通分量

求去掉每一个割点后剩下几个连通分量

就求割点那个算法 里面加点东西就行

cnt[i]代表如果i是割点 去掉后会有几个连通分量

根节点要有2个或以上的的子树才是割点 根是割点 那么cnt[root] = child（子树的个数）不是割点cnt[root] = 0;

#include <cstdio>
#include <cstring>
#include <vector>
#include <stack>
#include <algorithm>
using namespace std;
const int maxn = 1010;
vector <int> a[maxn], bcc[maxn];
int pre[maxn];
int low[maxn];
bool iscut[maxn];
int bccno[maxn];
int cnt[maxn];
int dfs_clock;
int bcc_cnt;
int n;

struct Edge
{
	int u, v;
};

stack <Edge> S;
int dfs(int u, int fa)
{
	int lowu = pre[u] = ++dfs_clock;
	int child = 0;
	for(int i = 0; i < a[u].size(); i++)
	{
		int v = a[u][i];
		Edge e = (Edge){u, v};
		if(!pre[v])
		{
			S.push(e);
			child++;
			int lowv = dfs(v, u);
			lowu = min(lowu, lowv);
			if(lowv >= pre[u])
			{
				iscut[u] = true;
				bcc_cnt++;
				bcc[bcc_cnt].clear();
				cnt[u]++;
				while(1)
				{
					Edge x = S.top();
					S.pop();
					if(bccno[x.u] != bcc_cnt)
					{
						bcc[bcc_cnt].push_back(x.u);
						bccno[x.u] = bcc_cnt;
					}
					if(bccno[x.v] != bcc_cnt)
					{
						bcc[bcc_cnt].push_back(x.v);
						bccno[x.v] = bcc_cnt;
					}
					if(x.u == u && x.v == v)
						break;
				}
			}
		}
		else if(pre[v] < pre[u] && v != fa)
		{
			S.push(e);
			lowu = min(lowu, pre[v]);
		}
	}
	if(fa < 0 && child == 1)
	{
		iscut[u] = false;
		cnt[u] = 0;
	}
	if(fa < 0 && child > 1)
	{
		iscut[u] = true;
		cnt[u] = child;
	}
	else if(cnt[u] > 0)
		cnt[u]++;
	return lowu;
}
void find_bcc()
{
	memset(cnt, 0, sizeof(cnt));
	memset(pre, 0, sizeof(pre));
	memset(iscut, 0, sizeof(iscut));
	memset(bccno, 0, sizeof(bccno));
	dfs_clock = bcc_cnt = 0;
	dfs(1, -1);
}
int main()
{
	int u, v;
	int cas = 0;
	while(scanf("%d", &u) && u)
	{
		scanf("%d", &v);
		n = 0;
		n = max(n, u);
		n = max(n, v);
		for(int i = 1; i <= 1000; i++)
			a[i].clear();
		
		a[u].push_back(v);
		a[v].push_back(u);
		while(scanf("%d", &u) && u)
		{
			scanf("%d", &v);
			a[u].push_back(v);
			a[v].push_back(u);
			n = max(n, u);
			n = max(n, v);
		}
		find_bcc();
		if(cas++)
			puts("");
		printf("Network #%d\n", cas);
		int flag = 0;
		for(int i = 1; i <= n; i++)
		{
			if(iscut[i])
			{
				printf("  SPF node %d leaves %d subnets\n", i, cnt[i]);
				flag++;	
			}
		}
		if(!flag)
			printf("  No SPF nodes\n");
		//printf("\n");
	}
	return 0;
}