树上最长不下降链 线段树合并+set

读错题了，然后写了一个树上 LIS，应该是对的吧......

code: 

#include <bits/stdc++.h>    
#define N 200005   
#define LL long long 
#define setIO(s) freopen(s".in","r",stdin) 
using namespace std;     
struct seg
{   
    #define lson t[x].ls 
    #define rson t[x].rs 
    int tot;    
    struct node 
    {
        int ls,rs,maxx;
    }t[N*50];       
    int newnode() { return ++tot; }   
    void update(int &x,int l,int r,int p,int v) 
    {
        if(!x) x=newnode();        
        t[x].maxx=max(t[x].maxx,v);   
        if(l==r) return;  
        int mid=(l+r)>>1;  
        if(p<=mid)   update(lson,l,mid,p,v); 
        else update(rson,mid+1,r,p,v); 
    }   
    int merge(int x,int y) 
    { 
        if(!x||!y) return x+y; 
        int now=newnode();        
        t[now].maxx=max(t[x].maxx,t[y].maxx);     
        t[now].ls=merge(t[x].ls,t[y].ls); 
        t[now].rs=merge(t[x].rs,t[y].rs); 
        return now;    
    }
    int query(int x,int l,int r,int L,int R) 
    { 
        if(!x) return 0; 
        if(l>=L&&r<=R)  return t[x].maxx;    
        int mid=(l+r)>>1,re=0;   
        if(L<=mid)  re=max(re, query(lson,l,mid,L,R));  
        if(R>mid)   re=max(re, query(rson,mid+1,r,L,R));   
        return re;     
    }
    #undef lson 
    #undef rson 
}in,de;  
multiset<int>s1,s2;  
multiset<int>::iterator it1,it2;  
int n,edges; 
int rt_in[N],rt_de[N],val[N],ans[N],A[N],hd[N],to[N<<1],nex[N<<1],max1[N],max2[N];    
void add(int u,int v) 
{
    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v;  
}
void dfs(int u,int ff) 
{  
    int max_in=1,max_de=1; 
    for(int i=hd[u];i;i=nex[i])  
    {           
        int v=to[i]; 
        if(v==ff) continue; 
        dfs(v,u);              
        max_in=max(max_in, in.query(rt_in[v],1,n,val[u],n)+1);        
        max_de=max(max_de, de.query(rt_de[v],1,n,1,val[u])+1);        
    }        
    int tl=0;  
    s1.clear(); 
    s2.clear();  
    for(int i=hd[u];i;i=nex[i])   
    { 
        int v=to[i]; 
        if(v==ff)    continue;               
        max1[++tl]=in.query(rt_in[v],1,n,val[u],n);   
        max2[tl]=de.query(rt_de[v],1,n,1,val[u]);               
        s1.insert(max1[tl]); 
        s2.insert(max2[tl]);  
    }    
    if(tl>1) 
    {     
        for(int i=1;i<=tl;++i) 
        {    
            s1.erase(s1.lower_bound(max1[i]));   
            s2.erase(s2.lower_bound(max2[i]));    
            it1=s1.end(), it2=s2.end();     
            it1--,it2--;   
            ans[u]=max(ans[u], max2[i]+(*it1)+1);   
            ans[u]=max(ans[u], max1[i]+(*it2)+1);    
            s1.insert(max1[i]); 
            s2.insert(max2[i]);     
        }
    }                
    ans[u]=max(ans[u],max(max_in,max_de));   
    in.update(rt_in[u],1,n,val[u],max_in);  
    de.update(rt_de[u],1,n,val[u],max_de);                      
    if(ff)  
    {    
        rt_in[ff]=in.merge(rt_in[ff],rt_in[u]);  
        rt_de[ff]=de.merge(rt_de[ff],rt_de[u]);  
    }       
}
int main() 
{ 
    // setIO("input");  
    int i,j;          
    scanf("%d",&n);  
    for(i=1;i<=n;++i)    scanf("%d",&val[i]), A[i]=val[i];   
    sort(A+1,A+1+n);  
    for(i=1;i<=n;++i)    val[i]=lower_bound(A+1,A+1+n,val[i])-A;        
    for(i=2;i<=n;++i) 
    {
        int x; 
        scanf("%d",&x); 
        add(x,i),add(i,x); 
    } 
    dfs(1,0);   
    int tmp=0; 
    for(i=1;i<=n;++i)   tmp=max(tmp,ans[i]); 
    printf("%d
",tmp); 
    return 0;   
}