[BZOJ4260]Codechef REBXOR(Trie)

Trie模板题。求出每个前缀和后缀的最大异或和区间，枚举断点就可。不知为何跑得飞快。

#include<cstdio>
#include<cstring>
#include<algorithm>
#define rep(i,l,r) for (int i=(l); i<=(r); i++)
using namespace std;

const int N=400010,M=N*30;
int n,nd,x,ans,a[N],pre[N],suf[N],ch[M][2];

void ins(int k){
    int x=1;
    for (int i=30; ~i; i--){
        if (!ch[x][(k>>i)&1]) ch[x][(k>>i)&1]=++nd;
        x=ch[x][(k>>i)&1];
    }
}

int que(int k){
    int x=1,res=0;
    for (int i=30; ~i; i--)
        if (ch[x][!((k>>i)&1)]) res|=1<<i,x=ch[x][!((k>>1)&1)];
            else x=ch[x][(k>>i)&1];
    return res;
}

int main(){
    freopen("bzoj4260.in","r",stdin);
    freopen("bzoj4260.out","w",stdout);
    scanf("%d",&n); nd=1; ins(0);
    rep(i,1,n) scanf("%d",&a[i]);
    rep(i,1,n-1) x^=a[i],pre[i]=max(pre[i-1],que(x)),ins(x);
    memset(ch,0,sizeof(ch)); nd=1; ins(0); x=0;
    for (int i=n; i>1; i--) x^=a[i],suf[i]=max(suf[i+1],que(x)),ins(x);
    rep(i,1,n-1) ans=max(ans,pre[i]+suf[i+1]);
    printf("%d\n",ans);
    return 0;
}