BZOJ 3166: [Heoi2013]Alo 链表+可持久化trie

链表这个东西非常好用啊 ~

code:

#include <bits/stdc++.h>
#define N 50010
#define inf 2000400000
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
int n,ans,cnt;
int a[N],t[N*35],ch[N*35][2],pre[N],nxt[N],rt[N];
pair<int,int>b[N];
void insert(int x,int pos)
{
    int now=rt[pos]=++cnt, last=rt[pos-1];
    for(int i=30;i>=0;--i)
    {
        int o=(x>>i)&1;
        ch[now][o^1]=ch[last][o^1];
        ch[now][o]=++cnt;
        t[ch[now][o]]=t[ch[last][o]]+1;
        now=ch[now][o];
        last=ch[last][o];
    }
}
int query(int sum,int l,int r)
{
    --l;
    int now=rt[l],last=rt[r],ret=0;
    for(int i=30;i>=0;--i)
    {
        int o=(sum>>i)&1;
        if(t[ch[last][o^1]]>t[ch[now][o^1]])
        {
            ret+=(1<<i);
            now=ch[now][o^1];
            last=ch[last][o^1];
        }
        else
        {
            now=ch[now][o];
            last=ch[last][o];
        }
    }
    return ret;
}
int main()
{
    // setIO("input");
    int i,j,n;
    scanf("%d",&n);
    int fir=0,last=n+1;
    a[fir]=a[last]=inf;
    for(i=1;i<=n;++i)
    {
        pre[i]=i-1, nxt[i]=i+1;
        scanf("%d",&a[i]), b[i]=make_pair(a[i],i), insert(a[i],i);
    }
    sort(b+1,b+1+n);
    for(i=1;i<=n;++i)
    {
        int x=b[i].second;
        int l=pre[x],r=nxt[x];
        nxt[l]=r,pre[r]=l;
        if(l!=fir)   ans=max(ans, query(a[x],pre[l]+1,r-1));
        if(r!=last)  ans=max(ans, query(a[x],l+1,nxt[r]-1));
    }
    printf("%d\n",ans);
    return 0;
}