> 5 8
> 1 2
> 1 3
> 2 4
> 3 2
> 4 3
> 4 5
> 5 4
> 2 1
> 
> ans : 5
我这组数据是对的，但没有ac，能不能帮忙看下，谢～
#include <cstdio>
#include <cstring>
#define maxe 500010
#define maxn 100010

using namespace std;

typedef struct node
{
	int x,y;
	int next;
}node;

int first[maxn+1],firstt[maxn+1],mark[maxn+1]={},seq[2*maxn+1];
node g[maxe+1],gt[maxe+1];
int num[maxn+1]={};
int n,e,total=0;

void add(int a,int b,int c)
{
	g[c].x = a; g[c].y = b; g[c].next = first[a];
	first[a] = c;
	
	gt[c].x = b; gt[c].y = a; gt[c].next = firstt[b];
	firstt[b] = c;
}

void init()
{
	int a,b;
	scanf("%d%d",&n,&e);
	for (int i=1;i<=n;i++)
		{
			first[i] = -1;
			firstt[i] = -1;
		}
	for (int i=1;i<=e;i++)
	{
		scanf("%d%d",&a,&b);
		add(a,b,i);
	}
}

void dfs(int x,node *g,int *first,int color)
{
	if (mark[x]) return;
	mark[x] = color;
	++num[color];
	total++;
	seq[total] = x;
	int temp;
	temp = first[x];
	while (temp!=-1)
	{
		dfs(g[temp].y,g,first,color);
		temp = g[temp].next;
	}
}

void work()
{
	int temp;
	int flag;
	int scc[maxn+1];
	int color=0,t1,t2;
	for (int i=1;i<=n;i++)
	if (!mark[i])
		dfs(i,g,first,1);
	memset(mark,0,sizeof(mark));
	memset(num,0,sizeof(num));
	for (int i=1;i<=n;i++)
	if (!mark[seq[i]])
		{
			color++;
			dfs(seq[i],gt,firstt,color);
			//printf("%d %d\n",i,color);
		}
	for (int i=1;i<=n;i++)
	{
		flag = 0;
		for (temp=first[i];temp!=-1;temp=g[temp].next)
		{
			if (mark[g[temp].y]!=mark[i])
				++flag;
		}
		scc[mark[i]] += flag;
		//printf("%d\n",flag);
	}
	t1 = -1;
	for (int i=1;i<=color;i++)
		{
			if (!scc[i])
				{
					++t1; t2 = num[i];
				}
		}	
	//printf("%d\n",t1);
	if (!t1) printf("%d\n",t2);
}

int main()
{
	init();
	work();
	return 0;
}