BZOJ 4260 REBXOR

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 400050
using namespace std;
int n,a[maxn],x[maxn],root,ls[maxn*32],rs[maxn*32],tot=0;
int mx[maxn],ans=0;
int read()
{
    char ch;int data=0;
    while (ch<‘0‘ || ch>‘9‘) ch=getchar();
    while (ch>=‘0‘ && ch<=‘9‘)
    {
        data=data*10+ch-‘0‘;
        ch=getchar();
    }
    return data;
}
int ask(int now,int val,int bit)
{
    if (!now) return 0;
    int ans=0;
    for (int i=bit;i>=0;i--)
    {
        int nb=val&(1<<i);
        if (!nb)
        {
            if (rs[now]) {now=rs[now];ans+=(1<<i);}
            else now=ls[now];
        }
        else
        {
            if (ls[now]) {now=ls[now];ans+=(1<<i);}
            else now=rs[now];
        }
    }
    return ans;
}
void modify(int now,int val,int bit)
{
    int pos=now;
    for (int i=bit;i>=0;i--)
    {
        int nb=val&(1<<i);
        if (!nb) {if (!ls[pos]) ls[pos]=++tot;pos=ls[pos];}
        else {if (!rs[pos]) rs[pos]=++tot;pos=rs[pos];}
    }
}
int main()
{
    n=read();tot=root=1;
    for (int i=1;i<=n;i++) {a[i]=read();x[i]=x[i-1]^a[i];}
    for (int i=1;i<=n;i++)
    {
        mx[i]=max(max(x[i],mx[i-1]),ask(root,x[i],30));
        modify(root,x[i],30);
    }
    for(int i=1;i<=tot;i++) ls[i]=rs[i]=0;
    tot=root=1;
    for (int i=n;i>=1;i--)
    {
        int ret=ask(root,x[i],30);
        ans=max(ans,ret+mx[i-1]);
        modify(root,x[i],30);
    }
    printf("%d\n",ans);
    return 0;
}