CCF 认证4

题意：求强联通分量

Tarjan算法

 #include<iostream>
 #include<stdio.h>
 #include<stdlib.h>
 #include<memory.h>
 #include<string.h>
 #include<algorithm>
 #include<cmath>
 #include<map>
 #define clc(a,b) memset(a,b,sizeof(a))
 typedef long double ld;
 typedef long long ll;
 const int N = ;
 const double eps=1e-;
 const int inf=-;
 const int maxn=1e5+;
 const int num=;
 const double Pi=acos(-);
 using namespace std;

 struct gragh
 {
     int to;
     int next;
 } V[num];

 bool instack[num]= {false};
 int low[num]= {},DFN[num]= {},Stap[num]= {},Belong[num]= {};
 int answer=;
 int Dindex,stop,Bcnt;
 int head[num];
 int edge;

 void add(int a,int b)
 {
     V[edge].to=b;
     V[edge].next=head[a];
     head[a]=edge++;

 }
 void tarjan(int u)
 {
     int v;
     DFN[u]=low[u]=++Dindex;
     instack[u]=true;
     Stap[stop++]=u;
     for(int i=head[u]; i!=-; i=V[i].next)
     {
         v=V[i].to;
         if(!DFN[v])
         {
             tarjan(v);
             if(low[v]<low[u])
                 low[u]=low[v];
         }
         else if(instack[v]&&DFN[v]<low[u])
             low[u]=DFN[v];
     }
     if(DFN[u]==low[u])
     {
         int sum=;
         Bcnt++;
         do
         {
             v=Stap[--stop];
             instack[v]=false;
             Belong[v]=Bcnt;
             sum++;
         }
         while(v!=u);
         cout<<sum<<endl;
         if(sum!=)
             answer+=(sum*(sum-))/;
     }
 }
 void solve(int N)
 {
     stop=Bcnt=Dindex=;
     // clc(DFN,0);
     for(int i=; i<=N; i++)
         if(!DFN[i])
             tarjan(i);
 }

 int main()
 {
     int n,m;
     int a,b;
     cin>>n>>m;
     clc(head,-);
     edge=;
     for(int i=; i<m; i++)
     {
         cin>>a>>b;
         add(a,b);
     }
     solve(n);
     cout<<answer<<endl;
     return ;
 }