11月10日联考 林檎花火

Posted 2020-11-29 dftmr

性质：删掉任意一个点后，原来能被删的点仍能被删，原来不能被删的点仍不能被删

判断每个点能否被删，并从小到大输出

#include<cstdio>
using namespace std;
int head[300005],len,a[300005],n,x,y,flag[300005],ans;
struct EDGE{
	int to,next;
}edge[600005];
void add(int x,int y){
	++len;
	edge[len].to=y;
	edge[len].next=head[x];
	head[x]=len;
}
void dfs1(int u,int fa){
	flag[u]=a[u];
	for (register int i=head[u];i;i=edge[i].next){
		int v=edge[i].to;
		if (v!=fa){
			dfs1(v,u);
			flag[u]&=a[v];
		}
	}
}
int main(){
	scanf ("%d",&n);
	for (register int i=2;i<=n;++i){
		scanf ("%d%d",&x,&a[i]);
		add(x,i);add(i,x);
	}
	dfs1(1,0);
	for (register int i=1;i<=n;++i){
		if (flag[i]) ++ans;
	}
	printf ("%d
",ans);
	for (register int i=1;i<=n;++i){
		if (flag[i]) printf ("%d ",i);
	}
	printf ("
");
	return 0;
}