强连通分量与缩点的模板题

之前一直不知道缩点是怎么回事 原来就是体现在belong[n]数组里了..

 

#include <bits/stdc++.h>
using namespace std;

struct node
{
    int v;
    int next;
};

stack <int> stk;
node edge[10010];
int first[10010],degree[10010];
int dfn[10010],low[10010],book[10010],belong[10010],sum[10010];
int n,m,cnt,num;

void addedge(int u,int v)
{
    edge[num].v=v;
    edge[num].next=first[u];
    first[u]=num++;
    return;
}

void calculate();
void dfs(int cur);

int main()
{
    int i,u,v;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        memset(first,-1,sizeof(first));
        num=0;
        for(i=1;i<=m;i++)
        {
            scanf("%d%d",&u,&v);
            addedge(u,v);
        }
        calculate();
    }
    return 0;
}

void calculate()
{
    int i,j,v,sum1,sum2,p;
    while(!stk.empty()) stk.pop();
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(book,0,sizeof(book));
    memset(belong,0,sizeof(belong));
    memset(sum,0,sizeof(sum));
    cnt=0,num=0;
    for(i=1;i<=n;i++)
    {
        if(dfn[i]==0)
        {
            dfs(i);
        }
    }
    memset(degree,0,sizeof(degree));
    for(i=1;i<=n;i++)
    {
        for(j=first[i];j!=-1;j=edge[j].next)
        {
            v=edge[j].v;
            if(belong[v]!=belong[i])
            {
                degree[belong[i]]++;
            }
        }
    }
    sum1=0,sum2=0;
    for(i=1;i<=num;i++)
    {
        if(sum[i]>1) sum1++;
        if(degree[i]==0)
        {
            sum2++;
            p=i;
        }
    }
    printf("%d\n",sum1);
    if(sum2==1&&sum[p]>1)
    {
        for(i=1;i<=n;i++)
        {
            if(belong[i]==p)
            {
                printf("%d ",i);
            }
        }
        printf("\n");
    }
    else
    {
        printf("-1\n");
    }
    return;
}

void dfs(int cur)
{
    int i,v;
    stk.push(cur);
    book[cur]=1;
    cnt++;
    dfn[cur]=cnt,low[cur]=cnt;
    for(i=first[cur];i!=-1;i=edge[i].next)
    {
        v=edge[i].v;
        if(dfn[v]==0)
        {
            dfs(v);
            if(low[v]<low[cur])
            {
                low[cur]=low[v];
            }
        }
        else
        {
            if(book[v]==1&&dfn[v]<low[cur])
            {
                low[cur]=dfn[v];
            }
        }
    }
    if(dfn[cur]==low[cur])
    {
        num++;
        while(!stk.empty())
        {
            v=stk.top();
            stk.pop();
            book[v]=0;
            belong[v]=num;
            sum[num]++;
            if(v==cur) break;
        }
    }
    return;
}