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 = 5005;
int n, a[MAXN], l[MAXN], r[MAXN], vis[MAXN], dp[MAXN];

int main()
{
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    for (int i = 1; i <= n; i++)
    {
        if (!l[a[i]]) l[a[i]] = i;
        r[a[i]] = i;
    }
    for (int i = 1; i <= n; i++)
    {
        dp[i] = dp[i - 1];
        int cur = 0;
        memset(vis, 0, sizeof(vis));
        int minL = l[a[i]]; 
        for (int j = i; j >= 1; j--)
        {
            if (r[a[j]] > i) break;
            if (!vis[a[j]]) vis[a[j]] = 1, cur ^= a[j];    
            minL = min(minL, l[a[j]]);
            if (minL >= j) dp[i] = max(dp[i], dp[j - 1] + cur);
        }    
    }        
    cout << dp[n] << endl;
    return 0;    
}