Tarjan强联通分量模板

Posted 2020-09-17

 1 #include <algorithm>
 2 #include <cstdio>
 3 
 4 using namespace std;
 5 
 6 const int N(100015);
 7 int n,m,v,u;
 8 int edgesum,head[N];
 9 
10 struct Edge
11 {
12     int from,to,next;
13     Edge(int from=0,int to=0,int next=0) :
14         from(from),to(to),next(next) {}
15 }edge[N];
16 int ins(int from,int to)
17 {
18     edge[++edgesum]=Edge(from,to,head[from]);
19     return head[from]=edgesum;
20 }
21 
22 int dfn[N],tim,low[N],vis[N];
23 int Stack[N],top,instack[N];
24 int col[N],colsum;
25 
26 void DFS(int now)
27 {
28     dfn[now]=low[now]=++tim; vis[now]=1;
29     Stack[++top]=now; instack[now]=1;
30     for(int i=head[now];i;i=edge[i].next)
31     {
32         int to=edge[i].to;
33         if(instack[to]) low[i]=min(low[i],dfn[to]);
34         else if(!vis[to])
35                 DFS(to),low[i]=min(low[i],low[to]);
36     }
37     if(low[now]==dfn[now])
38     {
39         colsum++;
40         col[now]=colsum;
41         for(;Stack[top]!=now;top--)
42         {
43             col[Stack[top]]=colsum;
44             instack[Stack[top]]=0;
45         }
46         instack[now]=0;
47         top--;
48     }
49 }
50 
51 int main()
52 {
53     scanf("%d%d",&n,&m);
54     for(;m--;)
55     {
56         scanf("%d%d",&u,&v);
57         ins(u,v);
58     }
59     for(int i=1;i<=n;i++)
60         if(!vis[i]) DFS(i);
61     return 0;
62 }