Problem p02734 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <complex>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>
using namespace std;
using ll = long long;

// Modint
struct Mint {
  static const ll mod = 998244353;
  ll val;

  Mint() { val = 0; }
  Mint(ll a) {
    val = a;
    verify_value();
  }

  void verify_value() {
    if (val >= mod)
      val %= mod;
    if (val < 0)
      val %= mod, val += mod;
  }

  Mint pow(ll p) const {
    Mint cur = Mint(val), ret = 1;
    while (p > 0) {
      if (p & 1)
        ret *= cur;
      cur *= cur;
      p >>= 1LL;
    }
    return ret;
  }
  Mint inv() const {
    if (val == 0)
      cerr << "WARNING: inv() is called with 0." << endl;
    return pow(mod - 2);
  }

  Mint operator+() const { return *this; }
  Mint operator-() const { return Mint(mod - val); }

  Mint operator+=(const Mint &a) {
    val += a.val;
    if (val >= mod)
      val -= mod;
    return Mint(val);
  }
  Mint operator*=(const Mint &a) {
    val *= a.val;
    if (val >= mod)
      val %= mod;
    return Mint(val);
  }
  Mint operator-=(const Mint &a) { return *this += -a; }
  Mint operator/=(const Mint &a) { return *this *= a.inv(); }

  Mint operator++() { return *this += Mint(1); }
  Mint operator--() { return *this -= Mint(1); }
  Mint operator++(int) {
    Mint ret = *this;
    ++(*this);
    return ret;
  }
  Mint operator--(int) {
    Mint ret = *this;
    --(*this);
    return ret;
  }

  operator ll() const { return val; }
};

Mint operator+(const Mint &a, const Mint &b) {
  ll ret = a.val + b.val;
  if (ret >= Mint::mod)
    ret -= Mint::mod;
  return Mint(ret);
}
Mint operator*(const Mint &a, const Mint &b) {
  ll ret = a.val * b.val;
  if (ret >= Mint::mod)
    ret %= Mint::mod;
  return Mint(ret);
}
Mint operator-(const Mint &a, const Mint &b) { return a + (-b); }
Mint operator/(const Mint &a, const Mint &b) { return a * b.inv(); }

ostream &operator<<(ostream &out, const Mint &a) { return out << a.val; }
istream &operator>>(istream &in, Mint &a) {
  in >> a.val;
  a.verify_value();
  return in;
}

Mint pow(Mint a, ll b) { return a.pow(b); }

// Combinatorics
constexpr int MAX_N = 2000003;
Mint fact[MAX_N], inv[MAX_N];

void init_fact() {
  fact[0] = inv[0] = 1;
  for (ll i = 1; i < MAX_N; i++) {
    fact[i] = fact[i - 1] * Mint(i);
    inv[i] = fact[i].inv();
  }
}

// aCb
Mint C(int a, int b) {
  if (a < b)
    return 0;
  Mint res = fact[a];
  res *= inv[b];
  res *= inv[a - b];
  return res;
}

// aPb
Mint P(int a, int b) {
  if (a < b)
    return 0;
  return fact[a] * inv[a - b];
}

// aHb
Mint H(int a, int b) {
  if (b == 0)
    return 1;
  return C(a + b - 1, b);
}

int main() {
  int n, s;
  cin >> n >> s;
  vector<int> a(n);
  for (int i = 0; i < n; i++)
    cin >> a[i];
  vector<Mint> cnt(3 * s);
  cnt[0] = 1;
  for (int i = 0; i < n; i++) {
    for (int j = s; j >= 0; j--) {
      Mint cf = 1;
      if (j == 0)
        cf *= i + 1;
      if (j + a[i] == s)
        cf *= n - i;
      cnt[j + a[i]] += cf * cnt[j];
    }
  }
  cout << cnt[s] << endl;
  return 0;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <complex>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>
using namespace std;
using ll = long long;

// Modint
struct Mint {
  static const ll mod = 998244353;
  ll val;

  Mint() { val = 0; }
  Mint(ll a) {
    val = a;
    verify_value();
  }

  void verify_value() {
    if (val >= mod)
      val %= mod;
    if (val < 0)
      val %= mod, val += mod;
  }

  Mint pow(ll p) const {
    Mint cur = Mint(val), ret = 1;
    while (p > 0) {
      if (p & 1)
        ret *= cur;
      cur *= cur;
      p >>= 1LL;
    }
    return ret;
  }
  Mint inv() const {
    if (val == 0)
      cerr << "WARNING: inv() is called with 0." << endl;
    return pow(mod - 2);
  }

  Mint operator+() const { return *this; }
  Mint operator-() const { return Mint(mod - val); }

  Mint operator+=(const Mint &a) {
    val += a.val;
    if (val >= mod)
      val -= mod;
    return Mint(val);
  }
  Mint operator*=(const Mint &a) {
    val *= a.val;
    if (val >= mod)
      val %= mod;
    return Mint(val);
  }
  Mint operator-=(const Mint &a) { return *this += -a; }
  Mint operator/=(const Mint &a) { return *this *= a.inv(); }

  Mint operator++() { return *this += Mint(1); }
  Mint operator--() { return *this -= Mint(1); }
  Mint operator++(int) {
    Mint ret = *this;
    ++(*this);
    return ret;
  }
  Mint operator--(int) {
    Mint ret = *this;
    --(*this);
    return ret;
  }

  operator ll() const { return val; }
};

Mint operator+(const Mint &a, const Mint &b) {
  ll ret = a.val + b.val;
  if (ret >= Mint::mod)
    ret -= Mint::mod;
  return Mint(ret);
}
Mint operator*(const Mint &a, const Mint &b) {
  ll ret = a.val * b.val;
  if (ret >= Mint::mod)
    ret %= Mint::mod;
  return Mint(ret);
}
Mint operator-(const Mint &a, const Mint &b) { return a + (-b); }
Mint operator/(const Mint &a, const Mint &b) { return a * b.inv(); }

ostream &operator<<(ostream &out, const Mint &a) { return out << a.val; }
istream &operator>>(istream &in, Mint &a) {
  in >> a.val;
  a.verify_value();
  return in;
}

Mint pow(Mint a, ll b) { return a.pow(b); }

// Combinatorics
constexpr int MAX_N = 2000003;
Mint fact[MAX_N], inv[MAX_N];

void init_fact() {
  fact[0] = inv[0] = 1;
  for (ll i = 1; i < MAX_N; i++) {
    fact[i] = fact[i - 1] * Mint(i);
    inv[i] = fact[i].inv();
  }
}

// aCb
Mint C(int a, int b) {
  if (a < b)
    return 0;
  Mint res = fact[a];
  res *= inv[b];
  res *= inv[a - b];
  return res;
}

// aPb
Mint P(int a, int b) {
  if (a < b)
    return 0;
  return fact[a] * inv[a - b];
}

// aHb
Mint H(int a, int b) {
  if (b == 0)
    return 1;
  return C(a + b - 1, b);
}

int main() {
  int n, s;
  cin >> n >> s;
  vector<int> a(n);
  for (int i = 0; i < n; i++)
    cin >> a[i];
  vector<Mint> cnt(n * s + 2);
  cnt[0] = 1;
  for (int i = 0; i < n; i++) {
    for (int j = s; j >= 0; j--) {
      Mint cf = 1;
      if (j == 0)
        cf *= i + 1;
      if (j + a[i] == s)
        cf *= n - i;
      cnt[j + a[i]] += cf * cnt[j];
    }
  }
  cout << cnt[s] << endl;
  return 0;
}