CF811C WA

#include <assert.h>
#include <bits/stdc++.h>
using namespace std;
#define dbg(...) logger(#__VA_ARGS__, __VA_ARGS__)
template <typename... Args> void logger(string vars, Args &&... values)
{
    cerr << vars << " = ";
    string delim = "";
    (..., (cerr << delim << values, delim = ", "));
    cerr << endl;
}

template <class T> using mpq = priority_queue<T, vector<T>, greater<T>>;
using ll = long long;
using pii = pair<int, int>;

int n;
map<int, pii> mg;
int a[1 << 13];
int xa[1 << 13];
int dp[1 << 13];

int main(int argc, char **argv)
{
    scanf("%d", &n);
    // memset(lm, 0x3F, sizeof(lm));
    // memset(dp, -1, sizeof(dp));
    for (int i = 1; i <= n; ++i) {
        scanf("%d", a + i), xa[i] = xa[i - 1] ^ a[i];
        if (mg.count(a[i]))
            mg[a[i]].second = i;
        else
            mg[a[i]] = {i, i};
    }
    for (int i = 1; i <= n; ++i) {
        dp[i] = dp[i - 1];
        int v = a[i];
        int l = mg[v].first, r = mg[v].second;
        if (r == i) {
            int xor_val = 0;
            set<int> vis;
            for (int k = l; k <= r; ++k) {
                int ak = a[k];
                if (vis.count(ak) == 0) {
                    vis.insert(ak);
                    xor_val ^= ak;
                }
            }
            dp[i] = max(dp[i], dp[l - 1] + xor_val);
            // dbg(v, l, r, dp[i], dp[l - 1], (xa[l] ^ xa[r - 1]));
            // dp[i] = max(dp[i], dp[l - 1] + (xa[l] ^ xa[r - 1]));
        }
    }
    printf("%d\n", dp[n]);
    return 0;
};