#include <bits/stdc++.h>
#define all(vec) vec.begin(), vec.end()
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
constexpr ll INF = (1LL << 30) - 1LL;
constexpr ll LINF = (1LL << 60) - 1LL;
constexpr double eps = 1e-9;
constexpr ll MOD = 1000000007LL;
template <typename T> bool chmin(T &a, T b) {
if (a > b) {
a = b;
return true;
}
return false;
};
template <typename T> bool chmax(T &a, T b) {
if (a < b) {
a = b;
return true;
}
return false;
};
template <typename T> ostream &operator<<(ostream &os, vector<T> v) {
for (int i = 0; i < v.size(); i++) {
os << v[i] << (i + 1 == v.size() ? "\n" : " ");
}
return os;
}
template <typename T> vector<T> make_v(size_t a) { return vector<T>(a); }
template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}
template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
t = v;
}
template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
for (auto &e : t) {
fill_v(e, v);
}
};
int main() {
cin.tie(0);
ios::sync_with_stdio(false);
int n;
cin >> n;
vector<int> a(n);
for (int i = 0; i < n; i++) {
cin >> a[i];
}
int x = 0;
if (n <= 4000) {
for (int i = 0; i < n; i++) {
for (int j = i; j < n; j++) {
x ^= (a[i] + a[j]);
}
}
} else {
vector<ll> co(4010);
for (int i = 0; i < n; i++) {
co[a[i]]++;
}
for (int i = 1; i <= 4000; i++) {
if (co[i] == 0) {
continue;
}
ll s = (co[i] - 1LL) * co[i] / 2LL + co[i];
if (s % 2) {
x ^= (i + j);
}
for (int j = i + 1; j <= 4000; j++) {
if (co[j] == 0 || co[i] % 2 == 0 || co[j] % 2 == 0) {
continue;
}
x ^= (i + j);
}
}
}
cout << x << endl;
}
Compilation message
xorsum.cpp: In function 'int main()':
xorsum.cpp:71:27: error: 'j' was not declared in this scope
x ^= (i + j);
^
