Tarjan algorithm of Double Unicom

Transferred from: https://www.zhihu.com/question/40746887/answer/88428236

There are three kinds of connected components: side double connected component, point double connected component, Strong connected component, the first two belong to undirected graph, the latter belongs to the graph

Defined:

The two connected components are divided into double connected component and edge double connected component. If an undirected graph removes any one of the nodes (an edge) does not change the connectivity of this graph, that is, there is no cut point (bridge), it is called a point (edge) double-connected graph. Each maximal point (edge) double-connected sub-graph in an undirected graph is called a point (edge) double-connected component of this undirected graph.

The code is as follows:

Point double unicom struct edge{int u,v; Edge (int _u,int _v): U (_u), V (_v) {}}edge[maxn];int dfn[maxn],low[maxn],cut[maxn],bccno[maxn];vector<int>gra[    Maxn],bcc[maxn];stack<int>stk;int cnt,bcnt;void Tarjan (int f,int u) {dfn[u]=low[u]=++cnt;    int child=0;    int sz=gra[u].size ();        for (int i=0;i<sz;i++) {int id=gra[u][i];        int v=edge[id].v;            if (!dfn[v]) {Stk.push (ID);            child++;            Tarjan (U,V);            Low[u]=min (Low[u],low[v]);                if (Low[v]>=dfn[u]) {cut[u]=1;                Bcc[++bcnt].clear ();                    while (1) {int id=stk.top ();                    Stk.pop ();                    int uu=edge[id].u;                    int vv=edge[id].v;                        if (bccno[uu]!=bcnt) {bcc[bcnt].push_back (UU);                    bccno[uu]=bcnt;            } if (bccno[vv]!=bcnt) {bcc[bcnt].push_back (vv);            bccno[vv]=bcnt;                    } if (uu==u&&vv==v) {break;            }}}}else if (dfn[v]<dfn[u]&&v!=f) {Stk.push (ID);        Low[u]=min (Low[u],dfn[v]);    }} if (f<0&&child==1) {cut[u]=0;    }} side Dual link struct edge{int u,v; Edge (int _u,int _v): U (_u), V (_v) {}}edge[maxn];int dfn[maxn],low[maxn],bccno[maxn];vector<int>gra[maxn],bcc[    Maxn];bool isb[maxn];void Tarjan (int f,int u) {dfn[u]=low[u]=++cnt;    int sz=gra[u].size ();        for (int i=0;i<sz;i++) {int id=gra[u][i];        int v=edge[id].v;            if (!dfn[v]) {Tarjan (u,v);            Low[u]=min (Low[u],low[v]);            if (Low[v]>dfn[u]) {isb[id]=isb[id^1]=1;        }}else if (dfn[v]<dfn[u]&&v!=f) {low[u]=min (low[u],dfn[v]);    }}}void dfs (int u) {dfn[u]=1;    bccno[u]=bcnt; int SZ=GRA[u].size ();        for (int i=0;i<sz;i++) {int id=gra[u][i];        int v=edge[id].v;        if (Isb[id]) {continue;        } if (!dfn[v]) {DFS (v);        }}}int Main () {for (int i=1;i<=n;i++) {if (!dfn[i]) {Tarjan ( -1,i);    }} memset (Dfn,0,sizeof (DFN));            for (int i=1;i<=n;i++) {if (!dfn[i]) {bcnt++;        DFS (i); }    }}

　　

Tarjan algorithm of Double Unicom