Problem p02838 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;

// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
//
// using namespace __gnu_pbds;
// template<typename T> using ordered_set = tree<T, null_type, less<T>,
// rb_tree_tag, tree_order_statistics_node_update>;

// class Timer {
//     clock_t start;
//     string name;
// public:
//     Timer() {name = "";start = clock();}
//     Timer(string s){name = s;start = clock();}
//     ~Timer() {fprintf(stderr, "%s: %.3gs\n", name.c_str(), 1.0*(clock() -
//     start) / CLOCKS_PER_SEC);}
// };

// #define isValid(a, b) ((a) >= 0 && (a) < (b))
// int dr[]  =  {0, -1, -1, -1,  0,  1, 1, 1};
// int dc[]  =  {1,  1,  0, -1, -1, -1, 0, 1};

#define all(x) (x).begin(), (x).end()
#define pb push_back
#define eb emplace_back
#define um unordered_map
#define us unordered_set
#define endl '\n'
#define what_is(x)                                                             \
  cerr << fixed << setprecision(2) << boolalpha << #x << " = " << x << endl

const double EPS = 1e-9;
const double PI = acos(-1.0);

template <typename T> inline T sq(T a) { return a * a; }
template <typename T1, typename T2> inline pair<T1, T2> mp(T1 a, T2 b) {
  return make_pair(a, b);
}
template <typename T1, typename T2> inline T1 safeMod(T1 a, T2 m) {
  return (a % m + m) % m;
} /*handling negative sign of remainder*/
template <typename T1, typename T2> inline bool isEq(T1 a, T2 b) {
  return abs(a - b) < EPS;
}
template <typename T1, typename T2, typename T3>
inline bool isEq(T1 a, T2 b, T3 eps) {
  return abs(a - b) < eps;
}
template <typename T> inline bool isKthBitOn(T n, int k) {
  assert(n <= numeric_limits<T>::max());
  assert(k <= numeric_limits<T>::digits);
  T ONE = 1;
  return bool((n & (ONE << k)));
}
template <typename T> inline void setKthBit(T &n, int k) {
  assert(n <= numeric_limits<T>::max());
  assert(k <= numeric_limits<T>::digits);
  T ONE = 1;
  n = (n | (ONE << k));
}
// mt19937 rng((int)chrono::steady_clock::now().time_since_epoch().count());
// template<typename T> inline T nextRand(T lo, T hi){return
// uniform_int_distribution<T>(lo, hi)(rng);}

#define toRad(deg) ((deg)*PI / 180.0)
#define toDeg(rad) ((rad)*180.0 / PI)

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;

const int oo = 0x3f3f3f3f;
const int MAX = 200010;
const int MOD = 1000000007;
const int precision = 10;

int sum[MAX][64];

ll binexp(ll b, int p) {
  ll ret = 1;
  while (p) {
    if (p & 1)
      ret = (ret * b) % MOD;
    b = (b * b) % MOD;
    p >>= 1;
  }
  return ret;
}

int main() {
  // assert(freopen("in.txt", "r", stdin));
  // assert(freopen("out.txt", "w", stdout));
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  // cout << fixed << setprecision(precision);
  int n;
  cin >> n;
  vector<ll> v(n);
  for (ll &x : v)
    cin >> x;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 62; j++) {
      if (isKthBitOn(v[i], j))
        sum[i][j] = 1;
    }
  }
  vector<int> bitsum(62);
  for (int j = 0; j < 62; j++) {
    int ss = 0;
    for (int i = 0; i < n; i++) {
      ss += sum[i][j];
    }
    bitsum[j] = ss;
  }
  ll ans = 0;
  ll div = binexp(2, MOD - 2);
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 62; j++) {
      if (isKthBitOn(v[i], j)) {
        ans = (ans + (1LL << j) % MOD * (n - bitsum[j]) % MOD) % MOD;
      } else {
        ans = (ans + (1LL << j) % MOD * bitsum[j] % MOD) % MOD;
      }
    }
  }
  cout << ans * div % MOD << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>

using namespace std;

// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
//
// using namespace __gnu_pbds;
// template<typename T> using ordered_set = tree<T, null_type, less<T>,
// rb_tree_tag, tree_order_statistics_node_update>;

// class Timer {
//     clock_t start;
//     string name;
// public:
//     Timer() {name = "";start = clock();}
//     Timer(string s){name = s;start = clock();}
//     ~Timer() {fprintf(stderr, "%s: %.3gs\n", name.c_str(), 1.0*(clock() -
//     start) / CLOCKS_PER_SEC);}
// };

// #define isValid(a, b) ((a) >= 0 && (a) < (b))
// int dr[]  =  {0, -1, -1, -1,  0,  1, 1, 1};
// int dc[]  =  {1,  1,  0, -1, -1, -1, 0, 1};

#define all(x) (x).begin(), (x).end()
#define pb push_back
#define eb emplace_back
#define um unordered_map
#define us unordered_set
#define endl '\n'
#define what_is(x)                                                             \
  cerr << fixed << setprecision(2) << boolalpha << #x << " = " << x << endl

const double EPS = 1e-9;
const double PI = acos(-1.0);

template <typename T> inline T sq(T a) { return a * a; }
template <typename T1, typename T2> inline pair<T1, T2> mp(T1 a, T2 b) {
  return make_pair(a, b);
}
template <typename T1, typename T2> inline T1 safeMod(T1 a, T2 m) {
  return (a % m + m) % m;
} /*handling negative sign of remainder*/
template <typename T1, typename T2> inline bool isEq(T1 a, T2 b) {
  return abs(a - b) < EPS;
}
template <typename T1, typename T2, typename T3>
inline bool isEq(T1 a, T2 b, T3 eps) {
  return abs(a - b) < eps;
}
template <typename T> inline bool isKthBitOn(T n, int k) {
  assert(n <= numeric_limits<T>::max());
  assert(k <= numeric_limits<T>::digits);
  T ONE = 1;
  return bool((n & (ONE << k)));
}
template <typename T> inline void setKthBit(T &n, int k) {
  assert(n <= numeric_limits<T>::max());
  assert(k <= numeric_limits<T>::digits);
  T ONE = 1;
  n = (n | (ONE << k));
}
// mt19937 rng((int)chrono::steady_clock::now().time_since_epoch().count());
// template<typename T> inline T nextRand(T lo, T hi){return
// uniform_int_distribution<T>(lo, hi)(rng);}

#define toRad(deg) ((deg)*PI / 180.0)
#define toDeg(rad) ((rad)*180.0 / PI)

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;

const int oo = 0x3f3f3f3f;
const int MAX = 300010;
const int MOD = 1000000007;
const int precision = 10;

int sum[MAX][64];

ll binexp(ll b, int p) {
  ll ret = 1;
  while (p) {
    if (p & 1)
      ret = (ret * b) % MOD;
    b = (b * b) % MOD;
    p >>= 1;
  }
  return ret;
}

int main() {
  // assert(freopen("in.txt", "r", stdin));
  // assert(freopen("out.txt", "w", stdout));
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  // cout << fixed << setprecision(precision);
  int n;
  cin >> n;
  vector<ll> v(n);
  for (ll &x : v)
    cin >> x;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 62; j++) {
      if (isKthBitOn(v[i], j))
        sum[i][j] = 1;
    }
  }
  vector<int> bitsum(62);
  for (int j = 0; j < 62; j++) {
    int ss = 0;
    for (int i = 0; i < n; i++) {
      ss += sum[i][j];
    }
    bitsum[j] = ss;
  }
  ll ans = 0;
  ll div = binexp(2, MOD - 2);
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 62; j++) {
      if (isKthBitOn(v[i], j)) {
        ans = (ans + (1LL << j) % MOD * (n - bitsum[j]) % MOD) % MOD;
      } else {
        ans = (ans + (1LL << j) % MOD * bitsum[j] % MOD) % MOD;
      }
    }
  }
  cout << ans * div % MOD << endl;
  return 0;
}