puzzle 期望树形DP

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>

#define ll long long
#define il inline
#define db double

using namespace std;

il int gi()
{
	int x=0,y=1;
	char ch=getchar();
	while(ch<‘0‘||ch>‘9‘)
		{
			if(ch==‘-‘)
				y=-1;
			ch=getchar();
		}
	while(ch>=‘0‘&&ch<=‘9‘)
		{
			x=x*10+ch-‘0‘;
			ch=getchar();
		}
	return x*y;
}

int head[1000045],cnt;
struct edge
{
	int next,to;
}e[1000045];

il void add(int from,int to)
{
	e[++cnt].next=head[from];
	e[cnt].to=to;
	head[from]=cnt;
}

bool vis[100045];

int size[100045];

db ans[100045];

void dfs1(int x)
{
	size[x]=1;
	int r=head[x];
	while(r!=-1)
		{
			int now=e[r].to;
			if(!vis[now])
				{
					vis[now]=1;
					dfs1(now);
					size[x]+=size[now];
				}
			r=e[r].next;
		}
}

void dfs2(int x)
{
	int r=head[x];
	while(r!=-1)
		{
			int now=e[r].to;
			if(!vis[now])
				{
					vis[now]=1;
					ans[now]=ans[x]+1+(size[x]-size[now]-1)/2.0;
					dfs2(now);
				}
			r=e[r].next;
		}
}

int main()
{
	memset(head,-1,sizeof(head));

	int n=gi();

	int x;
	for(int i=2;i<=n;i++)
		{
			x=gi();
			add(x,i);
		}
	
	vis[1]=1;
	dfs1(1);

	memset(vis,0,sizeof(vis));
	vis[1]=1;
	ans[1]=1.0;
	dfs2(1);

	for(int i=1;i<=n;i++)
		printf("%.1f ",ans[i]);

	return 0;
}