正解~（有大量注释）

#include<bits/stdc++.h>
using namespace std;
int v[1000001],l[1000001],r[1000001],fa[1000001],q[1000001],tot;//hey, give me some place to build!
bool dfs(int u1,int u2)
{
	if(v[u1]!=v[u2])//are you same at your value? no? bye bye!
		return false;
	if(l[u1]>0||r[u2]>0)//you have left kid or you have right kid? or all? 
	{
		if(!(l[u1]>0&&r[u2]>0))//oh... you are no same at kid! 
			return false;
		bool tmp=dfs(l[u1],r[u2]);//lets's check your kid.
		if(!tmp)//emmmmmm... naughty kid! go away!
			return false;
		tot+=2;//your size are bigger now:)
	}
	if(r[u1]>0||l[u2]>0)//same...
	{
		if(!(r[u1]>0&&l[u2]>0))
			return false;
		bool tmp=dfs(r[u1],l[u2]);
		if(!tmp)
			return false;
		tot+=2;
	}
	return true;//wonderful! AC!
}
bool check(int u)
{
	tot=1;
	if(l[u]==-1&&r[u]==-1)//you are the smallist!
		return true;
	else if(!(l[u]>0&&r[u]>0))//you are a bad guy...
		return false;
	tot=3;//great: you are a good one:)
	return dfs(l[u],r[u]);//check you now!
}
inline int read()//quike read is batter than scanf
{
	int x=0;
	char c;
	while((c=getchar())<'0'||c>'9')
		if(c=='-')
		{
			while((c=getchar())>='0'&&c<='9');
			return -1;//no kid:(
		}
	x=c-'0';
	while((c=getchar())>='0'&&c<='9')
		x=x*10+(c-'0');//build your kid:)
	return x;
}
int main()
{
	//freopen("tree.in","r",stdin);
	//freopen("tree.out","w",stdout);
	int n=read();
	for(int i=1;i<=n;i++)
		v[i]=read();//how much?
	for(int i=1;i<=n;i++)
	{
		l[i]=read();//your left kid?
		r[i]=read();//your right kid?
	}
	for(int i=1;i<=n;i++)
	{
		if(l[i]>0)
			fa[l[i]]=i;//who's your father?
		if(r[i]>0)
			fa[r[i]]=i;//who's your father?
	}
	int R;
	for(int i=1;i<=n;i++)
		if(!fa[i])//who's the ROOT?
		{
			R=i;
			break;
		}
	int f=1,e=1,ans=0;//ans must be the best!
	q[1]=R;//just wait and see!
	while(f<=e)
	{
		int u=q[f++];
		if(check(u))//good job, are you batter?
			ans=max(ans,tot);
		else//no, next one please.
		{
			if(l[u]>0)
				q[++e]=l[u];//your kid will go too
			if(r[u]>0)
				q[++e]=r[u];//your kid will go too
		}
	}
	printf("%d\n",ans);
	return 0;
}