洛谷 P3916 图的遍历(反向建边+DFS)
这道题很妙,用反向建边+DFS
#include<iostream>
#include<cstdio>
#include<cstring>
#define MAXN 100010
#define MAXM 200010
using namespace std;
int n,m,u,v,cnt,head[MAXN],A[MAXN];
struct Edge{
int to,nxt;
}edge[MAXM];
void addedge(int u,int v){
edge[cnt].to=v;edge[cnt].nxt=head[u];head[u]=cnt++;
}
void dfs(int u,int d){
if(A[u])return;
A[u]=d;
for(int i=head[u];i!=-1;i=edge[i].nxt){
int v=edge[i].to;
dfs(v,d);
}
}
int main(){
#ifdef WINE
freopen("data.in","r",stdin);
#endif
scanf("%d%d",&n,&m);
memset(head,-1,sizeof(head));
for(int i=0;i<m;i++){
scanf("%d%d",&u,&v);
addedge(v,u); // 反向建边
}
for(int i=n;i>=1;i--)dfs(i,i);
for(int i=1;i<=n;i++)printf("%d ",A[i]);
return 0;
}