51nod 最长递增子序列

#include<iostream>
#include<cstring>
#include<algorithm>
#define maxn 50050
using namespace std;
int n,ls[maxn<<2],rs[maxn<<2],val[maxn<<2],root,tot=0;
struct pnt
{
    int id,val;
}p[maxn];
bool cmp(pnt x,pnt y)
{
    if (x.val!=y.val) return x.val<y.val;
    return x.id>y.id;
}
void addpnt(int id,int val)
{
    p[id].id=id;
    p[id].val=val;
}
void build(int &now,int left,int right)
{
    now=++tot;val[now]=0;
    if (left==right) return;
    int mid=(left+right)>>1;
    build(ls[now],left,mid);
    build(rs[now],mid+1,right);
}
void pushup(int now)
{
    val[now]=max(val[ls[now]],val[rs[now]]);
}
int ask(int now,int left,int right,int l,int r)
{
    if ((left==l) && (right==r))
        return val[now];
    int mid=(left+right)>>1;
    if (r<=mid) return ask(ls[now],left,mid,l,r);
    else if (l>=mid+1) return ask(rs[now],mid+1,right,l,r);
    else return max(ask(ls[now],left,mid,l,mid),ask(rs[now],mid+1,right,mid+1,r));
}
void modify(int now,int left,int right,int pos,int x)
{
    if ((left==right) && (left==pos))
    {
        val[now]=x;
        return;
    }
    int mid=(left+right)>>1;
    if (pos<=mid) modify(ls[now],left,mid,pos,x);
    else modify(rs[now],mid+1,right,pos,x);
    pushup(now);
}
int main()
{
    scanf("%d",&n);
    build(root,1,n);
    for (int i=1;i<=n;i++)
    {
        int x;
        scanf("%d",&x);
        addpnt(i,x);
    }
    sort(p+1,p+n+1,cmp);
    for (int i=1;i<=n;i++)
    {
        int regis;
        if (p[i].id==1) regis=0;
        else regis=ask(root,1,n,1,p[i].id-1);
        modify(root,1,n,p[i].id,regis+1);
    }
    printf("%d\n",val[1]);
    return 0;
}