poj2186tarjan算法缩点求出度

#include <iostream>
#include <cstdio>
#include <string.h>
using namespace std;
const int maxn = 10005;
const int maxm = 100005;
struct node{
    int to,pre;
}e[maxm];
int n,m;
int idx;
int id[maxn],cnt;
int dfn[maxn],low[maxn];
int stack1[maxn],s_top;
int out[maxn];
int color[maxn];
int vis[maxn];
int cut_point = 0;
void init()
{
    memset(dfn,0,sizeof(dfn));
    memset(vis,0,sizeof(vis));
    memset(color,0,sizeof(color));
    memset(low,0,sizeof(low));
    memset(id,-1,sizeof(id));
    memset(out,0,sizeof(id));
    cnt = 0;
    idx = 0;
    s_top = 0;
    cut_point = 0;
}
void add(int u,int v)
{
    e[cnt].to = v;
    e[cnt].pre = id[u];
    id[u] = cnt++;
}
void tarjan(int u, int pre)
{
    dfn[u] = low[u] = ++idx;
    vis[u] = 1;
    stack1[s_top++] = u;

    for(int i = id[u];~i;i = e[i].pre)
    {
        int v = e[i].to;
        if(!vis[v])
        {
            tarjan(v,u);
            low[u] = min(low[v],low[u]);
        }
        else
        {
            low[u] = min(low[u],dfn[v]);
        }
    }
    if(low[u] == dfn[u])
    {
        cut_point++;//颜色1 。。。n
        while(s_top > 0 && stack1[s_top] != u)//目的是先处理完元素在判断是不是最后一个
        {
            s_top--;
            vis[stack1[s_top]] = 2;
            color[stack1[s_top]] = cut_point;
        }
    }
}

int main()
{
    int u,v;
    while(~scanf("%d%d",&n,&m))
    {
        //初始化
        init();
        //添加边
        for(int i = 0;i < m;i++)
        {
            scanf("%d%d",&u,&v);
            add(u,v);
        }
        //缩点处理——染色
        for(int i = 1;i <= n;i++)//防止不连通的情况
        {
            if(!vis[i])
            {
                tarjan(i,-1);
            }
        }
        //染色成功后，记录出度
        for(int i = 1;i <= n;i++)
        {
            for(int j = id[i];~j;j = e[j].pre)
            {
                int v = e[j].to;
                if(color[i] != color[v])
                {
                    ++out[color[i]];
                }
            }
        }
        //看看度为0的点的集合，找出所有的点
        //color还要一样，不能有两个
        int sum = 0,p_color;
        for(int i = 1;i <= cut_point;i++)
        {
            if(!out[i])
                sum++,p_color = i;
        }

        if(sum == 1)
        {
            int ans = 0;
            for(int i = 1;i <= n;i++)
            {
                if(color[i] == p_color)ans++;
            }
            printf("%d\n",ans);
        }
        else
        {
            puts("0");
        }
    }
    return 0;
}