邻接表

using namespace std;  

const int MAX = 100010;
  
struct {  
    int to,next,w;  
}edge[MAX];
  
int head[MAX];  
int cnt;
  
auto init=[](){  
    cnt=0;  
    memset(edge,0, sizeof(edge));  
    memset(head,-1, sizeof(head));  
	return nullptr;  
}(); 
 
void add(int u,int v){         
    edge[cnt].to=v;            //对于当前边的to进行更新
    edge[cnt].next=head[u];    //对链表方向进行操作,将原链表头加入
    head[u]=cnt++;             //更新链表头
}  

int main(){  
    freopen("1.txt","r",stdin);  
    freopen("2.txt","w",stdout);  
    int n,m,u,v;  
    scanf("%d %d",&n,&m);  
    for(int i=0;i<m;++i)  
        scanf("%d %d",&u,&v),add(u,v);  
    for(int i=1;i<=n;++i){//node 1-n   
        printf("%d : ",i);  
        for(int j=head[i];j!=-1;j=edge[j].next)  
            printf("%d->%d, ",i,edge[j].to);  
        printf("n");  
    }  
}