Problem p03051 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define ADD(a, b) a = (a + ll(b)) % mod
#define MUL(a, b) a = (a * ll(b)) % mod
#define MAX(a, b) a = max(a, b)
#define MIN(a, b) a = min(a, b)
#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
#define rer(i, a, b) for (int i = int(a) - 1; i >= int(b); i--)
#define all(a) (a).begin(), (a).end()
#define sz(v) (int)(v).size()
#define pb push_back
#define sec second
#define fst first
#define debug(fmt, ...) Debug(__LINE__, ":", fmt, ##__VA_ARGS__)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<int, pi> ppi;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> mat;
typedef complex<double> comp;
void Debug() { cerr << '\n'; }
template <class FIRST, class... REST> void Debug(FIRST arg, REST... rest) {
  cerr << arg << " ";
  Debug(rest...);
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  if (!v.empty()) {
    rep(i, 0, sz(v) - 1) out << v[i] << ", ";
    out << v.back();
  }
  out << "]";
  return out;
}
template <class S, class T>
ostream &operator<<(ostream &out, const pair<S, T> &v) {
  out << "(" << v.first << ", " << v.second << ")";
  return out;
}
const int MAX_N = 300010;
const int MAX_V = 100010;
const double eps = 1e-6;
const ll mod = 1000000007;
const int inf = 1 << 30;
const ll linf = 1LL << 60;
const double PI = 3.14159265358979323846;
mt19937 rng; // use it by rng() % mod, shuffle(all(vec), rng)
///////////////////////////////////////////////////////////////////////////////////////////////////

ll fac[MAX_N], inv[MAX_N], fiv[MAX_N]; // fiv:inv(fac(i))

ll mod_pow(ll a, ll n) {
  if (n == 0)
    return 1;
  ll res = mod_pow(a, n / 2);
  if (n % 2 == 0)
    return res * res % mod;
  else
    return a * res % mod * res % mod;
}

ll invf(ll a) { return mod_pow(a, mod - 2); }

void C_init(int n) {
  fac[0] = fac[1] = 1;
  inv[1] = 1;
  fiv[0] = fiv[1] = 1;
  rep(i, 2, n + 1) {
    fac[i] = fac[i - 1] * i % mod;
    inv[i] = mod - inv[mod % i] * (mod / i) % mod;
    fiv[i] = fiv[i - 1] * inv[i] % mod;
  }
}

ll C(int a, int b) { // assume a >= b
  if (a < b || a < 0 || b < 0)
    return 0;
  return fac[a] * fiv[b] % mod * fiv[a - b] % mod;
}

struct Ruiseki {
  int N;
  vector<ll> B;
  void init(int n) {
    N = n;
    B = vector<ll>(N + 1, 0);
  }
  Ruiseki() {}
  Ruiseki(int n) { init(n); }
  void add(int a, ll v) {
    if (a < 0 || N <= a)
      return;
    B[a + 1] += v;
  }
  void sweep() { rep(i, 1, N + 1) B[i] += B[i - 1]; }
  ll get(int a, int b) { //[a, b)
    if (a >= b)
      return 0;
    a = max(a, 0);
    b = min(b, N);
    return B[b] - B[a];
  }
};

int N;
vector<int> G[1 << 20];
int A[MAX_N];
Ruiseki rui;

void solve() {
  cin >> N;
  ll ans = 0;
  C_init(N);
  rui.init(N);
  rep(i, 0, N) cin >> A[i];
  int sum = 0, cnt = 1;
  rep(i, 0, N) {
    sum ^= A[i];
    if (sum == 0) {
      rui.add(i, 1);
      // debug(i);
      cnt++;
    } else
      G[sum].pb(i);
  }
  rui.sweep();
  // debug(sum, cnt);
  if (sum == 0) {
    ADD(ans, mod_pow(2, cnt - 2));
  }
  rep(i, 1, (1 << 20)) {
    if (sz(G[i]) == 0)
      continue;
    ll suma = 0, sumz = 1;
    // debug(G[i]);
    rep(j, 0, sz(G[i])) {
      // debug(i, j, suma, sumz);
      ll v = sumz;
      ADD(suma, v);
      if (j != sz(G[i]) - 1) {
        ll c = rui.get(G[i][j], G[i][j + 1]);
        ADD(sumz, suma * c % mod);
        // debug(G[i][j], G[i][j + 1], c);
      }
    }
    if (sum == 0) {
      ADD(ans, suma);
    } else if (sum == i) {
      ADD(ans, sumz);
    }
  }
  cout << ans << "\n";
}

uint32_t rd() {
  uint32_t res;
#ifdef __MINGW32__
  asm volatile("rdrand %0" : "=a"(res)::"cc");
#else
  res = std::random_device()();
#endif
  return res;
}

int main() {
#ifndef LOCAL
  ios::sync_with_stdio(false);
  cin.tie(0);
#endif
  cout << fixed;
  cout.precision(20);
  cerr << fixed;
  cerr.precision(6);
  rng.seed(rd());
#ifdef LOCAL
  // freopen("in.txt", "wt", stdout); //for tester
  freopen("in.txt", "rt", stdin);
#endif
  solve();
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define ADD(a, b) a = (a + ll(b)) % mod
#define MUL(a, b) a = (a * ll(b)) % mod
#define MAX(a, b) a = max(a, b)
#define MIN(a, b) a = min(a, b)
#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
#define rer(i, a, b) for (int i = int(a) - 1; i >= int(b); i--)
#define all(a) (a).begin(), (a).end()
#define sz(v) (int)(v).size()
#define pb push_back
#define sec second
#define fst first
#define debug(fmt, ...) Debug(__LINE__, ":", fmt, ##__VA_ARGS__)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<int, pi> ppi;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> mat;
typedef complex<double> comp;
void Debug() { cerr << '\n'; }
template <class FIRST, class... REST> void Debug(FIRST arg, REST... rest) {
  cerr << arg << " ";
  Debug(rest...);
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  if (!v.empty()) {
    rep(i, 0, sz(v) - 1) out << v[i] << ", ";
    out << v.back();
  }
  out << "]";
  return out;
}
template <class S, class T>
ostream &operator<<(ostream &out, const pair<S, T> &v) {
  out << "(" << v.first << ", " << v.second << ")";
  return out;
}
const int MAX_N = 500010;
const int MAX_V = 100010;
const double eps = 1e-6;
const ll mod = 1000000007;
const int inf = 1 << 30;
const ll linf = 1LL << 60;
const double PI = 3.14159265358979323846;
mt19937 rng; // use it by rng() % mod, shuffle(all(vec), rng)
///////////////////////////////////////////////////////////////////////////////////////////////////

ll fac[MAX_N], inv[MAX_N], fiv[MAX_N]; // fiv:inv(fac(i))

ll mod_pow(ll a, ll n) {
  if (n == 0)
    return 1;
  ll res = mod_pow(a, n / 2);
  if (n % 2 == 0)
    return res * res % mod;
  else
    return a * res % mod * res % mod;
}

ll invf(ll a) { return mod_pow(a, mod - 2); }

void C_init(int n) {
  fac[0] = fac[1] = 1;
  inv[1] = 1;
  fiv[0] = fiv[1] = 1;
  rep(i, 2, n + 1) {
    fac[i] = fac[i - 1] * i % mod;
    inv[i] = mod - inv[mod % i] * (mod / i) % mod;
    fiv[i] = fiv[i - 1] * inv[i] % mod;
  }
}

ll C(int a, int b) { // assume a >= b
  if (a < b || a < 0 || b < 0)
    return 0;
  return fac[a] * fiv[b] % mod * fiv[a - b] % mod;
}

struct Ruiseki {
  int N;
  vector<ll> B;
  void init(int n) {
    N = n;
    B = vector<ll>(N + 1, 0);
  }
  Ruiseki() {}
  Ruiseki(int n) { init(n); }
  void add(int a, ll v) {
    if (a < 0 || N <= a)
      return;
    B[a + 1] += v;
  }
  void sweep() { rep(i, 1, N + 1) B[i] += B[i - 1]; }
  ll get(int a, int b) { //[a, b)
    if (a >= b)
      return 0;
    a = max(a, 0);
    b = min(b, N);
    return B[b] - B[a];
  }
};

int N;
vector<int> G[1 << 20];
int A[MAX_N];
Ruiseki rui;

void solve() {
  cin >> N;
  ll ans = 0;
  C_init(N);
  rui.init(N);
  rep(i, 0, N) cin >> A[i];
  int sum = 0, cnt = 1;
  rep(i, 0, N) {
    sum ^= A[i];
    if (sum == 0) {
      rui.add(i, 1);
      // debug(i);
      cnt++;
    } else
      G[sum].pb(i);
  }
  rui.sweep();
  // debug(sum, cnt);
  if (sum == 0) {
    ADD(ans, mod_pow(2, cnt - 2));
  }
  rep(i, 1, (1 << 20)) {
    if (sz(G[i]) == 0)
      continue;
    ll suma = 0, sumz = 1;
    // debug(G[i]);
    rep(j, 0, sz(G[i])) {
      // debug(i, j, suma, sumz);
      ll v = sumz;
      ADD(suma, v);
      if (j != sz(G[i]) - 1) {
        ll c = rui.get(G[i][j], G[i][j + 1]);
        ADD(sumz, suma * c % mod);
        // debug(G[i][j], G[i][j + 1], c);
      }
    }
    if (sum == 0) {
      ADD(ans, suma);
    } else if (sum == i) {
      ADD(ans, sumz);
    }
  }
  cout << ans << "\n";
}

uint32_t rd() {
  uint32_t res;
#ifdef __MINGW32__
  asm volatile("rdrand %0" : "=a"(res)::"cc");
#else
  res = std::random_device()();
#endif
  return res;
}

int main() {
#ifndef LOCAL
  ios::sync_with_stdio(false);
  cin.tie(0);
#endif
  cout << fixed;
  cout.precision(20);
  cerr << fixed;
  cerr.precision(6);
  rng.seed(rd());
#ifdef LOCAL
  // freopen("in.txt", "wt", stdout); //for tester
  freopen("in.txt", "rt", stdin);
#endif
  solve();
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
  return 0;
}