Problem p02815 (C++)

Buggy submission (status: Time Limit Exceeded):
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

// template
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (a); i > (b); i--)
#define ALL(v) (v).begin(), (v).end()
typedef long long int ll;
const int inf = 0x3fffffff;
const ll INF = 0x1fffffffffffffff;
const double eps = 1e-12;
void tostr(ll x, string &res) {
  while (x)
    res += ('0' + (x % 10)), x /= 10;
  reverse(ALL(res));
  return;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
// template end

template <unsigned mod> struct mint {
  static int get_mod() { return mod; }
  int val;
  int inv() const {
    int tmp, a = val, b = mod, x = 1, y = 0;
    while (b)
      tmp = a / b, a -= tmp * b, swap(a, b), x -= tmp * y, swap(x, y);
    if (x < 0)
      x += mod;
    return x;
  }
  mint() : val(0) {}
  mint(ll x) : val(x >= 0 ? x % mod : mod + (x % mod)) {}
  mint pow(ll t) {
    mint res = 1, b = *this;
    while (t) {
      if (t & 1)
        res *= b;
      b *= b;
      t >>= 1;
    }
    return res;
  }
  mint &operator+=(const mint &x) {
    if ((val += x.val) >= mod)
      val -= mod;
    return *this;
  }
  mint &operator-=(const mint &x) {
    if ((val += mod - x.val) >= mod)
      val -= mod;
    return *this;
  }
  mint &operator*=(const mint &x) {
    val = (ll)val * x.val % mod;
    return *this;
  }
  mint &operator/=(const mint &x) {
    val = (ll)val * x.inv() % mod;
    return *this;
  }
  mint operator+(const mint &x) const { return mint(*this) += x; }
  mint operator-(const mint &x) const { return mint(*this) -= x; }
  mint operator*(const mint &x) const { return mint(*this) *= x; }
  mint operator/(const mint &x) const { return mint(*this) /= x; }
  bool operator==(const mint &x) const { return val == x.val; }
  bool operator!=(const mint &x) const { return val != x.val; }
};
using Mint = mint<1000000007>;
struct factorial {
  vector<Mint> Fact, Finv;

public:
  factorial(int maxx) {
    Fact.resize(maxx + 1), Finv.resize(maxx + 1);
    Fact[0] = Mint(1);
    rep(i, 0, maxx) Fact[i + 1] = Fact[i] * (i + 1);
    Finv[maxx] = Mint(1) / Fact[maxx];
    rrep(i, maxx, 0) Finv[i - 1] = Finv[i] * i;
  }
  Mint fact(int n, bool inv = 0) {
    if (inv)
      return Finv[n];
    else
      return Fact[n];
  }
  Mint nPr(int n, int r) {
    if (n < 0 || n < r || r < 0)
      return Mint(0);
    else
      return Fact[n] * Finv[n - r];
  }
  Mint nCr(int n, int r) {
    if (n < 0 || n < r || r < 0)
      return Mint(0);
    else
      return Fact[n] * Finv[r] * Finv[n - r];
  }
};

int main() {
  int n;
  scanf("%d", &n);
  vector<int> a(n);
  rep(i, 0, n) scanf("%d", &a[i]);
  sort(ALL(a));
  reverse(ALL(a));
  Mint coeff = Mint(2).pow(n - 1), add = Mint(2).pow(n - 2), res;
  rep(i, 0, n) {
    res += coeff * a[i];
    coeff += add;
  }
  res *= Mint(2).pow(n);
  printf("%d\n", res.val);
  return 0;
}

Fixed submission:
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

// template
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (a); i > (b); i--)
#define ALL(v) (v).begin(), (v).end()
typedef long long int ll;
const int inf = 0x3fffffff;
const ll INF = 0x1fffffffffffffff;
const double eps = 1e-12;
void tostr(ll x, string &res) {
  while (x)
    res += ('0' + (x % 10)), x /= 10;
  reverse(ALL(res));
  return;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
// template end

template <unsigned mod> struct mint {
  static int get_mod() { return mod; }
  int val;
  int inv() const {
    int tmp, a = val, b = mod, x = 1, y = 0;
    while (b)
      tmp = a / b, a -= tmp * b, swap(a, b), x -= tmp * y, swap(x, y);
    if (x < 0)
      x += mod;
    return x;
  }
  mint() : val(0) {}
  mint(ll x) : val(x >= 0 ? x % mod : mod + (x % mod)) {}
  mint pow(ll t) {
    mint res = 1, b = *this;
    while (t) {
      if (t & 1)
        res *= b;
      b *= b;
      t >>= 1;
    }
    return res;
  }
  mint &operator+=(const mint &x) {
    if ((val += x.val) >= mod)
      val -= mod;
    return *this;
  }
  mint &operator-=(const mint &x) {
    if ((val += mod - x.val) >= mod)
      val -= mod;
    return *this;
  }
  mint &operator*=(const mint &x) {
    val = (ll)val * x.val % mod;
    return *this;
  }
  mint &operator/=(const mint &x) {
    val = (ll)val * x.inv() % mod;
    return *this;
  }
  mint operator+(const mint &x) const { return mint(*this) += x; }
  mint operator-(const mint &x) const { return mint(*this) -= x; }
  mint operator*(const mint &x) const { return mint(*this) *= x; }
  mint operator/(const mint &x) const { return mint(*this) /= x; }
  bool operator==(const mint &x) const { return val == x.val; }
  bool operator!=(const mint &x) const { return val != x.val; }
};
using Mint = mint<1000000007>;
struct factorial {
  vector<Mint> Fact, Finv;

public:
  factorial(int maxx) {
    Fact.resize(maxx + 1), Finv.resize(maxx + 1);
    Fact[0] = Mint(1);
    rep(i, 0, maxx) Fact[i + 1] = Fact[i] * (i + 1);
    Finv[maxx] = Mint(1) / Fact[maxx];
    rrep(i, maxx, 0) Finv[i - 1] = Finv[i] * i;
  }
  Mint fact(int n, bool inv = 0) {
    if (inv)
      return Finv[n];
    else
      return Fact[n];
  }
  Mint nPr(int n, int r) {
    if (n < 0 || n < r || r < 0)
      return Mint(0);
    else
      return Fact[n] * Finv[n - r];
  }
  Mint nCr(int n, int r) {
    if (n < 0 || n < r || r < 0)
      return Mint(0);
    else
      return Fact[n] * Finv[r] * Finv[n - r];
  }
};

int main() {
  int n;
  scanf("%d", &n);
  vector<int> a(n);
  rep(i, 0, n) scanf("%d", &a[i]);
  if (n == 1) {
    Mint res = Mint(2) * a[0];
    printf("%d\n", res.val);
    return 0;
  }
  sort(ALL(a));
  reverse(ALL(a));
  Mint coeff = Mint(2).pow(n - 1), add = Mint(2).pow(n - 2), res;
  rep(i, 0, n) {
    res += coeff * a[i];
    coeff += add;
  }
  res *= Mint(2).pow(n);
  printf("%d\n", res.val);
  return 0;
}