Problem p02549 (C++) — buggy submission, verdict: Runtime Error

#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>
using namespace std;
using i32 = int_fast32_t;
using i64 = int_fast64_t;
using usize = uint_fast64_t;
#define rep(i, n) for (usize i = 0; i < (usize)(n); i++)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
using P = pair<i64, i64>;
constexpr i64 MAX = 10000000;
constexpr i64 MOD = 998244353;
i64 fac[MAX], finv[MAX], inv[MAX];

template <i64 modulus> class modcal {

public:
  i64 a;

  constexpr modcal(const i64 x = 0) noexcept : a(x % modulus) {}

  constexpr i64 &value() noexcept { return a; }

  constexpr const i64 &value() const noexcept { return a; }

  constexpr modcal operator+(const modcal rhs) const noexcept {
    return modcal(*this) += rhs;
  }

  constexpr modcal operator-(const modcal rhs) const noexcept {
    return modcal(*this) -= rhs;
  }

  constexpr modcal operator*(const modcal rhs) const noexcept {
    return modcal(*this) *= rhs;
  }

  constexpr modcal operator/(const modcal rhs) noexcept {
    return modcal(*this) /= rhs;
  }

  constexpr modcal &operator+=(const modcal rhs) noexcept {
    a += rhs.a;
    if (a >= modulus) {
      a -= modulus;
    }
    return *this;
  }

  constexpr modcal &operator-=(const modcal rhs) noexcept {
    if (a < rhs.a) {
      a += modulus;
    }
    a -= rhs.a;
    return *this;
  }

  constexpr modcal &operator*=(const modcal rhs) noexcept {
    a = a * rhs.a % modulus;
    return *this;
  }

  constexpr modcal &operator/=(modcal rhs) noexcept {
    i64 exp = modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }

  void COMninit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++) {
      fac[i] = fac[i - 1] * i % modulus;
      inv[i] = MOD - inv[modulus % i] * (modulus / i) % modulus;
      finv[i] = finv[i - 1] * inv[i] % modulus;
    }
  }

  i64 COMn(i64 n, i64 k) {
    if (n < k)
      return 0;
    if (n < 0 || k < 0)
      return 0;
    return fac[n] * (finv[k] * finv[n - k] % modulus) % modulus;
  }

  constexpr modcal<998244353> modpow(const modcal<998244353> &a, i64 n) {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t = t * t;
    if (n & 1)
      t = t * a;
    return t;
  }

  i64 modinv(i64 x) { // xy = 1となるyのうちMOD以下になるものを返す
    i64 m = MOD;
    i64 u = 1, v = 0;
    while (m) {
      i64 t = x / m;
      x -= t * m;
      swap(x, m);
      u -= t * v;
      swap(u, v);
    }
    u %= MOD;
    if (u < 0)
      u += MOD;
    return u;
  }
};

using modc = modcal<998244353>;

int main() {
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  i64 n, k;
  cin >> n >> k;
  vector<i32> l(k), r(k);
  rep(i, k) { cin >> l[i] >> r[i]; }
  vector<modc> dp(n + 1, 0);
  dp[1] = 1;
  vector<modc> imos(n + 1, 0);
  for (i32 i = 1; i <= n; i++) {
    imos[i] = imos[i] + imos[i - 1];
    dp[i] = dp[i] + imos[i];
    rep(j, k) {
      if (l[j] + i <= n)
        imos[l[j] + i] = imos[l[j] + i] + dp[i];
      if (r[j] + i + 1 <= n)
        imos[r[j] + i + 1] = imos[r[j] + i + 1] - dp[i];
    }
  }
  cout << dp[n].a << endl;
}

Error: -11

Fixed submission:

#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <cstdint>
#include <iostream>
#include <vector>

#include <cstddef>
using namespace std;
using i32 = int_fast32_t;
using i64 = int_fast64_t;
using usize = uint_fast64_t;
#define rep(i, n) for (usize i = 0; i < (usize)(n); i++)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
using P = pair<i64, i64>;
constexpr i64 MAX = 10000000;
constexpr i64 MOD = 1000000007;
i64 fac[MAX], finv[MAX], inv[MAX];

template <i64 modulus> class modcal {

public:
  i64 a;

  constexpr modcal(const i64 x = 0) noexcept : a(x % modulus) {}

  constexpr i64 &value() noexcept { return a; }

  constexpr const i64 &value() const noexcept { return a; }

  constexpr modcal operator+(const modcal rhs) const noexcept {
    return modcal(*this) += rhs;
  }

  constexpr modcal operator-(const modcal rhs) const noexcept {
    return modcal(*this) -= rhs;
  }

  constexpr modcal operator*(const modcal rhs) const noexcept {
    return modcal(*this) *= rhs;
  }

  constexpr modcal operator/(const modcal rhs) noexcept {
    return modcal(*this) /= rhs;
  }

  constexpr modcal &operator+=(const modcal rhs) noexcept {
    a += rhs.a;
    if (a >= modulus) {
      a -= modulus;
    }
    return *this;
  }

  constexpr modcal &operator-=(const modcal rhs) noexcept {
    if (a < rhs.a) {
      a += modulus;
    }
    a -= rhs.a;
    return *this;
  }

  constexpr modcal &operator*=(const modcal rhs) noexcept {
    a = a * rhs.a % modulus;
    return *this;
  }

  constexpr modcal &operator/=(modcal rhs) noexcept {
    i64 exp = modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }

  void COMninit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++) {
      fac[i] = fac[i - 1] * i % modulus;
      inv[i] = MOD - inv[modulus % i] * (modulus / i) % modulus;
      finv[i] = finv[i - 1] * inv[i] % modulus;
    }
  }

  i64 COMn(i64 n, i64 k) {
    if (n < k)
      return 0;
    if (n < 0 || k < 0)
      return 0;
    return fac[n] * (finv[k] * finv[n - k] % modulus) % modulus;
  }

  constexpr modcal<1000000007> modpow(const modcal<1000000007> &a, i64 n) {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t = t * t;
    if (n & 1)
      t = t * a;
    return t;
  }

  i64 modinv(i64 x) { // xy = 1となるyのうちMOD以下になるものを返す
    i64 m = MOD;
    i64 u = 1, v = 0;
    while (m) {
      i64 t = x / m;
      x -= t * m;
      swap(x, m);
      u -= t * v;
      swap(u, v);
    }
    u %= MOD;
    if (u < 0)
      u += MOD;
    return u;
  }
};

using modc = modcal<998244353>;

int main() {
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  i32 n, k;
  cin >> n >> k;
  vector<i32> imos(n + 1);
  rep(i, k) {
    i32 l, r;
    cin >> l >> r;
    imos[l]++;
    imos[r + 1]--;
  }
  vector<i32> rec;
  rep(i, n) {
    imos[i + 1] += imos[i];
    if (imos[i + 1])
      rec.emplace_back(i + 1);
  }
  vector<vector<modc>> dp(rec.size(), vector<modc>(n + 1));
  rep(i, rec.size()) { dp[i][1] = 1; }
  rep(i, rec.size()) {
    for (i32 j = rec[i] + 1; j <= n; j++)
      if (i == 0) {
        dp[i][j] = dp[i][j - rec[i]];
      } else {
        dp[i][j] = dp[i][j - rec[i]] + dp[i - 1][j - rec[i]] + dp[i - 1][j];
      }
  }
  cout << dp[rec.size()][n].a << endl;
}