TOJ 2018 POJ 1523 SPF / 割点

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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;}

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