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 = 30;
const double eps=1e-9;
const int inf=-100000;
const int maxn=1e5+10;
const int num=10001;
const double Pi=acos(-1);
using namespace std;

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

bool instack[num]= {false};
int low[num]= {0},DFN[num]= {0},Stap[num]= {0},Belong[num]= {0};
int answer=0;
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!=-1; 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=0;
        Bcnt++;
        do
        {
            v=Stap[--stop];
            instack[v]=false;
            Belong[v]=Bcnt;
            sum++;
        }
        while(v!=u);
        cout<<sum<<endl;
        if(sum!=0)
            answer+=(sum*(sum-1))/2;
    }
}
void solve(int N)
{
    stop=Bcnt=Dindex=0;
    // clc(DFN,0);
    for(int i=1; i<=N; i++)
        if(!DFN[i])
            tarjan(i);
}

int main()
{
    int n,m;
    int a,b;
    cin>>n>>m;
    clc(head,-1);
    edge=0;
    for(int i=0; i<m; i++)
    {
        cin>>a>>b;
        add(a,b);
    }
    solve(n);
    cout<<answer<<endl;
    return 0;
}