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\n",tmp);
    return 0;
}