CF811C Vladik and Memorable Trip

思路：

令dp[i]表示前i个的最大舒适度。则如果区间[j, i](1 < j <= i)满足条件，有如下转移：dp[i] = max(dp[i], dp[j - 1] + cur)。其中，cur为区间[j, i]的舒适度。

实现：

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 using namespace std;

 const int MAXN = ;
 int n, a[MAXN], l[MAXN], r[MAXN], vis[MAXN], dp[MAXN];

 int main()
 {
     cin >> n;
     for (int i = ; i <= n; i++)
         cin >> a[i];
     for (int i = ; i <= n; i++)
     {
         if (!l[a[i]]) l[a[i]] = i;
         r[a[i]] = i;
     }
     for (int i = ; i <= n; i++)
     {
         dp[i] = dp[i - ];
         int cur = ;
         memset(vis, , sizeof(vis));
         int minL = l[a[i]];
         for (int j = i; j >= ; j--)
         {
             if (r[a[j]] > i) break;
             if (!vis[a[j]]) vis[a[j]] = , cur ^= a[j];
             minL = min(minL, l[a[j]]);
             if (minL >= j) dp[i] = max(dp[i], dp[j - ] + cur);
         }
     }
     cout << dp[n] << endl;
     return ;
 }