只有90分，求大佬答疑

#include<iostream>
#include<string>
#include<string.h>
#include<algorithm>
#include<vector>
#include<queue>
#include<stack>
#include<map>
#include<cmath>
using namespace std;

#define ll long long
#define vec vector<int>
#define inf 0x3f3f3f3f
#define MAX 500005
#define P pair<ll,ll>
#define MOD 1000000007

int main() {
	int n, a[MAX], sum[MAX];
	while (cin >> n) {
		sum[0] = 0;
		map<int, vec> m; m[0].push_back(0);
		for (int i = 0; i < n; i++)
		{
			cin >> a[i];
			sum[i + 1] = sum[i] ^ a[i];
			m[sum[i + 1]].push_back(i + 1);
		}
		int res = 0;
		int des = 0;
		for (map<int, vec>::iterator k = m.begin(); k != m.end(); k++) {
			vec t = (*k).second;
			if (t.size() <= 1)continue;
			for (int i = 0; i < t.size(); i++)
				for (int j = i + 1; j < t.size(); j++)
					if ((t[j] - t[i]) % 2 == 0)
						res++;
		}
		cout << ...