强联通

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struct Tarjan:Graph{//强连通分量缩点
int low[maxn],dfn[maxn],belong[maxn],stk[maxn],instk[maxn],block[maxn];
int step,color;
void tarjan(){
step=color=0;
for(int i=0;i<=n;i++) dfn[i]=0;
for(int i=1;i<=n;i++) if(dfn[i]==0) tarjan(i,0);//多个联通快
}
void tarjan(int u,int father=0){//此函数不开放
low[u]=dfn[u]=++step; stk[++stk[0]]=u;instk[u]=1;
for(int i=head[u];~i;i=edge[i].nex){
int v=edge[i].v;
if(dfn[v]) {
if(instk[v]) low[u]=min(low[u],dfn[v]);
}
else{
tarjan(v,u);
low[u]=min(low[u],low[v]);
}
}
if(low[u]==dfn[u]){
block[color+1]=1;
while(stk[stk[0]]!=u) {
belong[stk[stk[0]]]=color+1;
instk[stk[stk[0]--]]=0;
block[color+1]++;
}
belong[stk[stk[0]]]=++color;
instk[stk[stk[0]--]]=0;
}
}
void rebuild(Dag&dag){
set<long long>se;
dag.ini(color);
for(int u=1;u<=n;u++){
int uu=belong[u];
for(int i=head[u];~i;i=edge[i].nex){
int v=edge[i].v;
int vv=belong[v];
if(uu==vv||se.find(uu*1e6+vv)!=se.end())continue;
se.insert(uu*1e6+vv);
dag.add_edge(uu,vv);
}
dag.dp[uu][u]=1;
dag.w[uu]=block[uu];
}
}
}graph;

点双联通

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struct Graph{
static const int maxn=1e5+5, maxm=3e5+5;
struct star{int v,nex;}edge[maxm<<1];
int head[maxn],cnt,n;
void ini(int n){
this->n=n; cnt=-1;
for(int i=0;i<=n;i++) head[i]=-1;
}
void add_edge(int u,int v){
edge[++cnt]=star{v,head[u]}; head[u]=cnt;
edge[++cnt]=star{u,head[v]}; head[v]=cnt;
}
}tree;

struct Tarjan:Graph{//割点
int low[maxn],dfn[maxn],cut[maxn];
int step;
void tarjan(){
step=0;
for(int i=0;i<=n;i++) dfn[i]=cut[i]=0;
for(int i=1;i<=n;i++) if(dfn[i]==0) tarjan(i,0);//多个联通快
}
void tarjan(int u,int father=0){//此函数不开放
low[u]=dfn[u]=++step;
int first=1, son=0;
for(int i=head[u];~i;i=edge[i].nex){
int v=edge[i].v;
if(v==father&&!first) first=false;
else if(dfn[v]) low[u]=min(low[u],dfn[v]);
else{
son++;
tarjan(v,u);
low[u]=min(low[u],low[v]);
//一个顶点u是割点,当且仅当1或2
//1.u为树根且u有多与一个子树
//2.u不为树根且存在边(u,v)为树边,使得dfn[u]<=low[v]
if(father!=0&&dfn[u]<=low[v]) cut[u]=1;
if(father==0&&son>1) cut[u]=1;
}
}
}
}graph;

边双联通

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struct Graph{
static const int maxn=1e5+5, maxm=3e5+5;
struct star{int v,nex;}edge[maxm<<1];
int head[maxn],cnt;
void ini(int n){
for(int i=0;i<=n;i++) head[i]=-1;
cnt=-1;
}
void add_edge(int u,int v){
edge[++cnt]=star{v,head[u]};
head[u]=cnt;
edge[++cnt]=star{u,head[v]};
head[v]=cnt;
}
};

struct Tarjan:Graph{//双联通分量, 割边, 桥, 边双联通缩点
struct Bridge{int u,v;}bridge[maxn];
int dfn[maxn],low[maxn],belong[maxn],vis[maxn],sta[maxn],sta_,nums,bridge_;
void ini(int n){
for(int i=0;i<=n;i++) vis[i]=0;
bridge_=0;
nums=0;
Graph::ini(n);
}
void tarjan(int u,int father,int&step){
low[u]=dfn[u]=++step;
sta[++sta_]=u;
vis[u]=1;
bool firsttimes=true;//用于判重边
for(int i=head[u];~i;i=edge[i].nex){
int v=edge[i].v;
if(v==father&&firsttimes) {
firsttimes=false;
continue;
}//父边
if(vis[v]==1) low[u]=min(low[u],dfn[v]);//回边,终点在栈中
else {//树边
tarjan(v,u,step);
low[u]=min(low[u],low[v]);
if(low[v]>dfn[u]) bridge[++bridge_]=Bridge{u,v};
}
}
if(low[u]==dfn[u]){
while(sta[sta_]!=u) belong[sta[sta_--]]=nums+1;
belong[sta[sta_--]]=++nums;
}
}
}graph;