BZOJ 3166 Alo

处理出每个数最靠近它的左右两个比它大的数。

然后可持久化trie。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 200050
#define inf 1000000007
using namespace std;
struct num
{
    int val,id;
}p[maxn];
int n,a[maxn];
int seg_ls[maxn<<2],seg_rs[maxn<<2],val1[maxn<<2],val2[maxn<<2],seg_root,seg_tot=0,l1[maxn],l2[maxn],r1[maxn],r2[maxn];
int tree[maxn*50][2],sum[maxn*50],root[maxn],bitt[35],ans=0,tot=0;
bool cmp(num x,num y)
{
    return x.val>y.val;
}
void get_table()
{
    bitt[0]=1;
    for (int i=1;i<=30;i++)
        bitt[i]=bitt[i-1]*2;
}
void build_seg(int &now,int left,int right)
{
    now=++seg_tot;val1[now]=0;val2[now]=inf;
    if (left==right) return;
    int mid=(left+right)>>1;
    build_seg(seg_ls[now],left,mid);
    build_seg(seg_rs[now],mid+1,right);
}
int ask_seg(int now,int left,int right,int pos,int type)
{
    if (left==right)
    {
        if (type==1) return val1[now];
        else return val2[now]; 
    }
    int mid=(left+right)>>1;
    if (type==1)
    {
        if (pos<=mid) return max(val1[now],ask_seg(seg_ls[now],left,mid,pos,type));
        else return max(val1[now],ask_seg(seg_rs[now],mid+1,right,pos,type));
    }
    else
    {
        if (pos<=mid) return min(val2[now],ask_seg(seg_ls[now],left,mid,pos,type));
        else return min(val2[now],ask_seg(seg_rs[now],mid+1,right,pos,type));
    }
}
void modify_seg(int now,int left,int right,int l,int r,int x,int type)
{
    if ((left==l) && (right==r))
    {
        if (type==1) val1[now]=max(val1[now],x);
        else val2[now]=min(val2[now],x);
        return;
    }    
    int mid=(left+right)>>1;
    if (r<=mid) modify_seg(seg_ls[now],left,mid,l,r,x,type);
    else if (l>=mid+1) modify_seg(seg_rs[now],mid+1,right,l,r,x,type);
    else
    {
        modify_seg(seg_ls[now],left,mid,l,mid,x,type);
        modify_seg(seg_rs[now],mid+1,right,mid+1,r,x,type);
    }
}
void work(int x)
{
    l1[p[x].id]=ask_seg(seg_root,1,n,p[x].id,1);
    if (l1[p[x].id]==0) l2[p[x].id]=0;
    else
    {
        if (l1[p[x].id]==1) l2[p[x].id]=0;
        else l2[p[x].id]=ask_seg(seg_root,1,n,l1[p[x].id]-1,1);
    }
    r1[p[x].id]=ask_seg(seg_root,1,n,p[x].id,2);
    if (r1[p[x].id]==inf) {r1[p[x].id]=n+1;r2[p[x].id]=n+1;}
    else
    {
        if (r1[p[x].id]==n) r2[p[x].id]=n+1;
        else r2[p[x].id]=ask_seg(seg_root,1,n,r1[p[x].id]+1,2);
        if (r2[p[x].id]==inf) r2[p[x].id]=n+1;
    }
    modify_seg(seg_root,1,n,p[x].id,n,p[x].id,1);
    modify_seg(seg_root,1,n,1,p[x].id,p[x].id,2);
}
void insert(int b,int last,int &now,int x)
{
    now=++tot;
    tree[now][0]=tree[last][0];tree[now][1]=tree[last][1];
    sum[now]=sum[last]+1;
    if (b==-1) return;
    int tmp=x&bitt[b];tmp>>=b;
    insert(b-1,tree[last][tmp],tree[now][tmp],x);
}
int ask(int b,int last,int now,int x)
{
    if (b==-1) return 0;
     int tmp=x&bitt[b];tmp>>=b;
    int r=sum[tree[now][tmp^1]]-sum[tree[last][tmp^1]];
    if (r>0) return ask(b-1,tree[last][tmp^1],tree[now][tmp^1],x)+bitt[b];
    else return ask(b-1,tree[last][tmp],tree[now][tmp],x);
}
int main()
{
    get_table();
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
        p[i].val=a[i];p[i].id=i;
    }
    sort(p+1,p+n+1,cmp);
    build_seg(seg_root,1,n);
    for (int i=1;i<=n;i++)
        work(i);
    for (int i=1;i<=n;i++)
        insert(30,root[i-1],root[i],a[i]);
    for (int i=1;i<=n;i++)
    {
        int l,r;
        l=l2[i]+1;r=r1[i]-1;
        ans=max(ans,ask(30,root[l-1],root[r],a[i]));
        l=l1[i]+1;r=r2[i]-1;
        ans=max(ans,ask(30,root[l-1],root[r],a[i]));
    }
    printf("%d\n",ans);
    return 0;
}