【BZOJ4260】Codechef REBXOR

题面

http://darkbzoj.tk/problem/4260

题解

#include<cstdio>
#include<iostream>
#include<cstring>
#define ri register int
#define N 400050
#define INF (1<<30)
using namespace std;

int n,L[N],R[N];
int a[N],sum1[N],sum2[N];

inline int dit(int x,int i){
  if (x&(1<<i)) return 1; else return 0;
}

struct TRIE {
  int ch[N*30][2],tot;
  void init() {tot=0;}
  void clear() {
    for (ri i=0;i<=tot;i++) ch[i][0]=ch[i][1]=0;
    tot=0;
  }
  void insert(int x) {
    int now=0;
    for (ri i=30;i>=0;i--) {
      int d=dit(x,i);
      if (!ch[now][d]) ch[now][d]=++tot;
      now=ch[now][d];
    }
  }
  int search(int x) {
    int ret=0,now=0;
    for (ri i=30;i>=0;i--) {
      int d=1^dit(x,i);
      if (ch[now][d]) now=ch[now][d],ret+=(1<<i); else now=ch[now][d^1];
    }
    return ret;
  }
} trie;

int main(){
  scanf("%d",&n);
  for (ri i=1;i<=n;i++) scanf("%d",&a[i]);
  for (ri i=1;i<=n;i++) sum1[i]=sum1[i-1]^a[i];
  for (ri i=n;i>=1;i--) sum2[i]=sum2[i+1]^a[i];
  trie.init();
  trie.clear();
  for (ri i=1;i<=n;i++) {
    trie.insert(sum1[i-1]);
    L[i]=trie.search(sum1[i]);
    L[i]=max(L[i],L[i-1]);
  }
  trie.clear();
  for (ri i=n;i>=1;i--) {
    trie.insert(sum2[i+1]);
    R[i]=trie.search(sum2[i]);
    R[i]=max(R[i],R[i+1]);
  }
  long long ret=0;
  for (ri i=1;i<n;i++) if (L[i]+R[i+1]>ret) ret=L[i]+R[i+1];
  cout<<ret<<endl;
}