bzoj 3166 [Heoi2013]Alo 可持久化字典树

次大值可以用过二分加rmq方法求出，左右边求出后会形成两个区间，然后直接上可持久化字典树。

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;
const int maxn=50005;
int root[maxn];
int cnt;
int fa[50];
namespace  Trie{
    int sum[maxn*32];
    int ch[maxn*32][2];
    void init(){
        memset(ch,0,sizeof(ch));
        memset(sum,0,sizeof(sum));
    }
    void insert(int pre,int no,int val){
        for(int i=30;i>=0;i--){
            ch[no][0]=ch[pre][0];
            ch[no][1]=ch[pre][1];
            sum[no]=sum[pre]+1;
            int w=(val>>i)&1;
            ch[no][w]=++cnt;
            no=ch[no][w];
            pre=ch[pre][w];
        }
        sum[no]=sum[pre]+1;
    }
    int query(int pre,int no,int val){
        int s=0;
        for(int i=30;i>=0;i--){
            int w=(val>>i)&1;
            if(sum[ch[no][w^1]]-sum[ch[pre][w^1]]>0){
                s+=fa[i];
                w=w^1;
            }
            no=ch[no][w];
            pre=ch[pre][w];
        }
        return s;
    }
}
int maxl[maxn][16];
void S_table(int n)
{
    int l = int(log((double)n)/log(2.0));
    for (int j=1;j<=l;j++)
    {
        for (int i=1; i + (1 << (j-1) ) - 1 <=n;++i)
        {
            maxl[i][j] = max(maxl[i][j-1], maxl[i + (1 << (j-1) )][j-1]);
        }
    }
}

int rmq(int l, int r)
{
    int k = int(log((double)(r-l+1))/log(2.0));
    int a1 = max(maxl[l][k], maxl[r - (1<<k) + 1][k]);
    return a1;
}
int a[maxn];
int main()
{
    for(int i=0;i<=30;i++)fa[i]=1<<i;
    int n;
    cnt=0;
    cin>>n;
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
        root[i]=++cnt;
        Trie::insert(root[i-1],root[i],a[i]);
        maxl[i][0]=a[i];
    }
    S_table(n);
    int ans=0;
    for(int i=1;i<=n;i++){
        int le=1,ri=i-1;
        while(le<=ri){
            int mid=(le+ri)/2;
            if(rmq(mid,i-1)>a[i]) le=mid+1;
            else ri=mid-1;
        }
        int l1=ri;
        int l2=0;
        if(ri>1){
            le=1;
            ri=l1-1;
            while(le<=ri){
                int mid=(le+ri)/2;
                if(rmq(mid,l1-1)>a[i]) le=mid+1;
                else ri=mid-1;
            }
            l2=ri;
        }
        le=i+1,ri=n;
        while(le<=ri){
            int mid=(le+ri)/2;
            if(rmq(i+1,mid)>a[i]) ri=mid-1;
            else le=mid+1;
        }
        int r1=le;
        int r2=n+1;
        if(r1<n){
            le=r1+1,ri=n;
            while(le<=ri){
                int mid=(le+ri)/2;
                if(rmq(r1+1,mid)>a[i]) ri=mid-1;
                else le=mid+1;
            }
            r2=le;
        }
        if(l1>=1){
            ans=max(ans,Trie::query(root[l2],root[r1-1],a[i]));
        }
        if(r1<=n){
            ans=max(ans,Trie::query(root[l1],root[r2-1],a[i]));
        }
    }
    cout<<ans<<endl;
}