hihocoder1860 最大异或和

思路：

把N个前缀异或和插入一棵trie树中，然后对每个前缀异或和x计算能使x ^ y最大的前缀异或和y。利用了异或运算的a ^ b ^ a = b的性质。

参考了https://cloud.tencent.com/developer/article/1343206

实现：

 #include <iostream>
 using namespace std;

 const int INF = 0x3f3f3f3f;
 const int N = ;
 int a[N], cnt = ;

 struct trieNode
 {
     trieNode * next[];
 }; 

 trieNode pool[N * ];

 trieNode * createTrie()
 {
     trieNode * root = &pool[cnt++];
     for (int i = ; i < ; i++)
     {
         root->next[i] = NULL;
     }
     return root;
 } 

 void insert(trieNode * root, int x)
 {
     trieNode * tmp = root;
     int index;
     for (int i = ; i >= ; i--)
     {
         int msk = ( << i);
         if (msk & x) index = ;
         else index = ;
         if (tmp->next[index] == NULL)
         {
             tmp->next[index] = createTrie();
         }
         tmp = tmp->next[index];
     }
 }

 int search(trieNode * root, int x)
 {
     trieNode * tmp = root;
     int res = ;
     for (int i = ; i >= ; i--)
     {
         int msk =  << i;
         int need;
         if (msk & x) need = ;
         else need = ;
         if (i == ) need =  - need;
         if (tmp->next[need])
         {
             res += (need << i);
             tmp = tmp->next[need];
         }
         else
         {
             res += ( - need << i);
             tmp = tmp->next[ - need];
         }
     }
     return x ^ res;
 }

 int main()
 {
     int n;
     while (cin >> n)
     {
         cnt = ;
         trieNode * root = createTrie();
         for (int i = ; i <= n; i++)
         {
             cin >> a[i];
             a[i] = a[i - ] ^ a[i];
             insert(root, a[i]);
         }
         insert(root, );
         int ans = -INF;
         for (int i = ; i <= n; i++)
         {
             ans = max(ans, search(root, a[i]));
         }
         cout << ans << endl;
     }
     return ;
 }