指针版邻接表

比起数组优点有三：

1.代码量少

2.fch再也不用想着清-1，不用纠结反向弧

3.更好理解了

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<queue>
#include<cstring>
#define PAU putchar(' ')
#define ENT putchar('
')
using namespace std;
const int maxn=100000+10,maxm=100000+10,inf=-1u>>1;
struct BFS{
    struct ted{int x,y;ted*next;}adj[maxm],*fch[maxn],*ms;
    bool vis[maxn];int n;
    void init(int n){
        this->n=n;ms=adj;memset(vis,false,sizeof(vis));return;
    }
    void ade(int u,int v){*ms=(ted){u,v,fch[u]};fch[u]=ms++;return;}
    void bfs(int x){
        queue<int>Q;Q.push(x);vis[x]=true;
        while(!Q.empty()){
            int u=Q.front();Q.pop();
            for(ted*e=fch[u];e;e=e->next){
                int v=e->y;if(!vis[v]) vis[v]=true,Q.push(v);
            }
        } return;
    }
}p1,p2;
inline int read(){
    int x=0,sig=1;char ch=getchar();
    while(!isdigit(ch)){if(ch=='-')sig=-1;ch=getchar();}
    while(isdigit(ch))x=10*x+ch-'0',ch=getchar();
    return x*=sig;
}
inline void write(int x){
    if(x==0){putchar('0');return;}if(x<0)putchar('-'),x=-x;
    int len=0,buf[15];while(x)buf[len++]=x%10,x/=10;
    for(int i=len-1;i>=0;i--)putchar(buf[i]+'0');return;
}
int n,m;
void init(){
    n=read();m=read();
    p1.init(n);p2.init(n);
    int x,y;
    for(int i=1;i<=m;i++){
        x=read();y=read();
        p1.ade(x,y);
        p2.ade(y,x);
    } p1.bfs(1);p2.bfs(1);
    for(int i=1;i<=n;i++){
        if(p1.vis[i]&&p2.vis[i]) write(i),ENT;
    } 
    return;
}
void work(){
    return;
}
void print(){
    return;
}
int main(){init();work();print();return 0;}