2208. [JSOI2010]连通数【Tarjan】

 1 #include<iostream>
 2 #include<cstring>
 3 #include<cstdio>
 4 #define N (2000+10)
 5 using namespace std;
 6 struct node
 7 {
 8     int to,next;
 9 }edge[N*N*2];
10 int Dfn[N],dfs_num,Color[N],col_num;
11 int vis[N],stack[N],top,Low[N];
12 int n,ans,head[N],num_edge;
13 char s[N];
14 
15 void add(int u,int v)
16 {
17     edge[++num_edge].to=v;
18     edge[num_edge].next=head[u];
19     head[u]=num_edge;
20 }
21 
22 void Tarjan(int x)
23 {
24     Dfn[x]=Low[x]=++dfs_num;
25     vis[x]=true;
26     stack[++top]=x;
27     for (int i=head[x];i;i=edge[i].next)
28         if (!Dfn[edge[i].to])
29         {
30             Tarjan(edge[i].to);
31             Low[x]=min(Low[x],Low[edge[i].to]);
32         }
33         else
34             if (vis[edge[i].to])
35                 Low[x]=min(Low[x],Dfn[edge[i].to]);
36     if (Dfn[x]==Low[x])
37     {
38         vis[x]=false;
39         Color[x]=++col_num;
40         while (stack[top]!=x)
41         {
42             vis[stack[top]]=false;
43             Color[stack[top--]]=col_num;
44         }
45         top--;
46     }
47 }
48 
49 
50 int main()
51 {
52     scanf("%d",&n);
53     for (int i=1;i<=n;++i)
54     {
55         scanf("%s",s);
56         for (int j=1;j<=n;++j)
57             if (s[j-1]==‘1‘)
58                 add(i,j);
59     }
60     for (int i=1;i<=n;++i)
61         if (!Dfn[i])
62             Tarjan(i);
63     for (int i=1;i<=n;++i)
64         for (int j=1;j<=n;++j)
65             if (Color[i]==Color[j])
66                 ++ans;
67     printf("%d",ans);
68 }