不能说是我水平厉害了吧

只是以前做过的题还是有点熟练的..

1A

算法:scc一遍

然后求哪些点没出度然后就行了

代码:

#include<set>
#include<map>
#include<list>
#include<queue>
#include<stack>
#include<math.h>
#include<string>
#include<time.h>
#include<bitset>
#include<vector>
#include<memory>
#include<utility>
#include<stdio.h>
#include<sstream>
#include<fstream>
#include<iostream>
#include<stdlib.h>
#include<string.h>
#include<algorithm>
using namespace std;
struct edge
{
    int y;
    edge * next;
};
edge * li[100005];
edge * new_edge()
{
    static edge a[100005];
    static int top=0;
    return &a[top++];
}
void insert_edge(int x,int y)
{
    edge * t=new_edge();
    t->y=y;
    t->next=li[x];
    li[x]=t;
}
int dfn[100005],low[100005];
int belong_to[100005];
bool inque[100005];
int tot;
void scc(int x)
{
    static int num=0;
    static int que[100005];
    dfn[x]=num;
    low[x]=num;
    num++;
    static int now=0;
    que[now++]=x;
    inque[x]=true;
    edge * t;
    for (t=li[x];t!=0;t=t->next)
    {
        if (dfn[t->y]==-1)
        {
            scc(t->y);
            low[x]=min(low[t->y],low[x]);
        }
        else if (inque[t->y])
        {
            low[x]=min(dfn[t->y],low[x]);
        }
    }
    if (dfn[x]==low[x])
    {
        for (;;)
        {
            now--;
            int t=que[now];
            inque[t]=false;
            belong_to[t]=tot;
            if (que[now]==x)
            {
                break;
            }
        }
        tot++;
    }
}
bool cannot[100005];
int main()
{
    #ifdef absi2011
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    #endif
    int n,m;
    scanf("%d%d",&n,&m);
    int i;
    for (i=0;i<m;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        x--;
        y--;
        insert_edge(x,y);
    }
    memset(dfn,-1,sizeof(dfn));
    for (i=0;i<n;i++)
    {
        if (dfn[i]==-1) scc(i);
    }
    for (i=0;i<n;i++)
    {
        edge * t;
        for (t=li[i];t!=0;t=t->next)
        {
            if (belong_to[i]!=belong_to[t->y])
            {
                cannot[belong_to[i]]=true;
                break;
            }
        }
    }
    int onlyans=-2;
    for (i=0;i<tot;i++)
    {
        if (!cannot[i])
        {
            if (onlyans!=-2)
            {
                onlyans=-1;
            }
            else
            {
                onlyans=i;
            }
        }
    }
    if (onlyans==-1)
    {
        puts("0");
        return 0;
    }
    int sum=0;
    for (i=0;i<n;i++)
    {
        if (onlyans==belong_to[i])
        {
            sum++;
        }
    }
    printf("%d\n",sum);
    return 0;
}