华硕ac5300最牛设置_acwing是什么

输入样例：
3 3
1 2
2 1
2 3
输出样例：
1

#include<bits/stdc++.h>
using namespace std;
const int N = 1e4 + 10;
const int M = 5e4 + 10;
struct Edge{ 
   
    int v,next,w;
}edge[M];
int head[N],cnt;
int low[N],num[N],dfn;
int sccno[N],sta[N],bcc,top;
bool in_stack[N];
int out[N],Size[N];
void add(int u,int v){ 
   
    edge[cnt].v = v;
    edge[cnt].next = head[u];
    head[u] = cnt ++;
}
void Tarjan(int u){ 
   
    low[u] = num[u] = ++ dfn;
    sta[top ++] = u,in_stack[u] = true;
    for(int i = head[u];~i;i = edge[i].next){ 
   
        int v = edge[i].v;
        if(!num[v]){ 
   
            Tarjan(v);
            low[u] = min(low[u],low[v]);
        }
        else if(in_stack[v])
            low[u] = min(low[u],num[v]);
    }
    if(low[u] == num[u]){ 
   
        bcc ++;
        int t;
        do{ 
   
            Size[bcc] ++;
            t = sta[-- top];
            in_stack[t] = false;
            sccno[t] = bcc;
        }while(t != u);
    }
}

int main(){ 
   
    memset(head,-1,sizeof head);
    int n,m;
    cin>>n>>m;
    int x,y;
    for(int i = 0;i < m;i ++){ 
   
        cin>>x>>y;
        add(x,y);
    }
    for(int i = 1;i <= n;i ++){ 
   
        if(!num[i])Tarjan(i);
    }
    for(int i = 1;i <= n;i ++){ 
   
        for(int j = head[i];~j;j = edge[j].next){ 
   
            int a = sccno[i],b = sccno[edge[j].v];
            if(a != b)out[a] ++;
        }
    }
    int count = 0;
    int c = 0;
    for(int i = 1;i <= bcc;i ++){ 
   
        if(!out[i]){ 
   
            c ++;
        
            count += Size[i];
        }
    }
    if(c == 1)cout<<count<<endl;
    else cout<<0<<endl;
    return 0;
}