Problem p02734 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define ll long long
#define V vector<long long>
#define VV vector<vector<long long>>
#define VVV vector<vector<vector<long long>>>
#define P pair<ll, ll>
#define rep(i, n) for (ll(i) = 0; (i) < (n); ++(i))
using namespace std;

long long mod = 998244353;
struct mint {
  long long x;
  mint(long long x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(long long t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

int main() {
  ll n, s;
  cin >> n >> s;
  V a(n);
  rep(i, n) cin >> a[i];
  vector<vector<mint>> dp(n + 1, vector<mint>(s + 1, 0));
  mint ans = 0;
  rep(i, n) {
    dp[i][0] += 1;
    rep(j, s + 1) {
      dp[i + 1][j] += dp[i][j];
      if (j + a[i] <= s + 1)
        dp[i + 1][j + a[i]] += dp[i][j];
    }
    ans += dp[i + 1][s];
  }
  cout << ans << endl;
}


Fixed submission:
#include <bits/stdc++.h>
#define ll long long
#define V vector<long long>
#define VV vector<vector<long long>>
#define VVV vector<vector<vector<long long>>>
#define P pair<ll, ll>
#define rep(i, n) for (ll(i) = 0; (i) < (n); ++(i))
using namespace std;

long long mod = 998244353;
struct mint {
  long long x;
  mint(long long x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(long long t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

int main() {
  ll n, s;
  cin >> n >> s;
  V a(n);
  rep(i, n) cin >> a[i];
  vector<vector<mint>> dp(n + 1, vector<mint>(s + 1, 0));
  mint ans = 0;
  rep(i, n) {
    dp[i][0] += 1;
    rep(j, s + 1) {
      dp[i + 1][j] += dp[i][j];
      if (j + a[i] <= s)
        dp[i + 1][j + a[i]] += dp[i][j];
    }
    ans += dp[i + 1][s];
  }
  cout << ans << endl;
}