Problem p02549 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < n; i++)
#define ll long long
using namespace std;
typedef pair<int, int> P;
typedef pair<ll, ll> LP;
const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
const int INF = 1000000000;
const ll LINF = 1000000000000000000; // 1e18
const ll MOD = 1000000007;
const ll MOD2 = 998244353;
const double PI = acos(-1.0);
const double EPS = 1e-10;

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

/*  ----------------------- DEBUG FUNCTION ---------------------------- */
#define DUMPOUT cerr
void dump_function() { DUMPOUT << ' '; }
void dump_function(bool a) { DUMPOUT << a; }
void dump_function(int a) { DUMPOUT << a; }
void dump_function(long long a) { DUMPOUT << a; }
void dump_function(char a) { DUMPOUT << a; }
void dump_function(string &a) { DUMPOUT << a; }
void dump_function(double a) { DUMPOUT << a; }
template <class T> void dump_function(const vector<T> &);
template <class T, size_t size> void dump_function(const array<T, size> &);
template <class T, class L> void dump_function(const pair<T, L> &p);
template <class T, size_t size> void dump_function(const T (&)[size]);
template <class T> void dump_function(const vector<T> &a) {
  if (a.empty())
    return;
  dump_function(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    DUMPOUT << " ";
    dump_function(*i);
  }
  DUMPOUT << endl;
}
template <class T> void dump_function(const deque<T> &a) {
  if (a.empty())
    return;
  dump_function(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    DUMPOUT << " ";
    dump_function(*i);
  }
}
template <class T, size_t size> void dump_function(const array<T, size> &a) {
  dump_function(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    DUMPOUT << " ";
    dump_function(*i);
  }
}
template <class T, class L> void dump_function(const pair<T, L> &p) {
  DUMPOUT << '(';
  dump_function(p.first);
  DUMPOUT << ",";
  dump_function(p.second);
  DUMPOUT << ')';
}
template <class T> void dump_function(set<T> &x) {
  for (auto e : x)
    dump_function(e), DUMPOUT << " ";
  DUMPOUT << endl;
}
template <class T> void dump_function(multiset<T> &x) {
  for (auto e : x)
    dump_function(e), DUMPOUT << " ";
  DUMPOUT << endl;
}
template <class T, size_t size> void dump_function(const T (&a)[size]) {
  dump_function(a[0]);
  for (auto i = a; ++i != end(a);) {
    DUMPOUT << " ";
    dump_function(*i);
  }
}
template <class T> void dump_function(const T &a) { DUMPOUT << a; }
int dump_out() {
  DUMPOUT << '\\n';
  return 0;
}
template <class T> int dump_out(const T &t) {
  dump_function(t);
  DUMPOUT << '\\n';
  return 0;
}
template <class Head, class... Tail>
int dump_out(const Head &head, const Tail &...tail) {
  dump_function(head);
  DUMPOUT << ' ';
  dump_out(tail...);
  return 0;
}

#ifdef DEBUG_
#define dump(x)                                                                \\
  DUMPOUT << #x << ": ";                                                       \\
  dump_function(x);                                                            \\
  DUMPOUT << endl;
void dumps() {}
template <class T> void dumps(const T &t) {
  dump_function(t);
  DUMPOUT << " ";
}
template <class Head, class... Tail>
void dumps(const Head &head, const Tail &...tail) {
  dump_function(head);
  DUMPOUT << ' ';
  dump_out(tail...);
}
#else
#define dump(x)
template <class... T> void dumps(const T &...) {}
#endif
/*  ----------------------- DEBUG FUNCTION ---------------------------- */

template <int MOD> struct Fp {
  long long val;
  constexpr Fp(long long v = 0) noexcept : val(v % MOD) {
    if (val < 0)
      val += MOD;
  }
  constexpr int getmod() { return MOD; }
  constexpr Fp operator-() const noexcept { return val ? MOD - val : 0; }
  constexpr Fp operator+(const Fp &r) const noexcept { return Fp(*this) += r; }
  constexpr Fp operator-(const Fp &r) const noexcept { return Fp(*this) -= r; }
  constexpr Fp operator*(const Fp &r) const noexcept { return Fp(*this) *= r; }
  constexpr Fp operator/(const Fp &r) const noexcept { return Fp(*this) /= r; }
  constexpr Fp &operator+=(const Fp &r) noexcept {
    val += r.val;
    if (val >= MOD)
      val -= MOD;
    return *this;
  }
  constexpr Fp &operator-=(const Fp &r) noexcept {
    val -= r.val;
    if (val < 0)
      val += MOD;
    return *this;
  }
  constexpr Fp &operator*=(const Fp &r) noexcept {
    val = val * r.val % MOD;
    return *this;
  }
  constexpr Fp &operator/=(const Fp &r) noexcept {
    long long a = r.val, b = MOD, u = 1, v = 0;
    while (b) {
      long long t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    val = val * u % MOD;
    if (val < 0)
      val += MOD;
    return *this;
  }
  constexpr bool operator==(const Fp &r) const noexcept {
    return this->val == r.val;
  }
  constexpr bool operator!=(const Fp &r) const noexcept {
    return this->val != r.val;
  }
  friend constexpr ostream &operator<<(ostream &os, const Fp<MOD> &x) noexcept {
    return os << x.val;
  }
  friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, long long n) noexcept {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t = t * t;
    if (n & 1)
      t = t * a;
    return t;
  }
};

template <class T> struct BiCoef {
  vector<T> fact_, inv_, finv_;
  constexpr BiCoef() {}
  constexpr BiCoef(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
    init(n);
  }
  constexpr void init(int n) noexcept {
    fact_.assign(n, 1), inv_.assign(n, 1), finv_.assign(n, 1);
    int MOD = fact_[0].getmod();
    for (int i = 2; i < n; i++) {
      fact_[i] = fact_[i - 1] * i;
      inv_[i] = -inv_[MOD % i] * (MOD / i);
      finv_[i] = finv_[i - 1] * inv_[i];
    }
  }
  constexpr T com(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[k] * finv_[n - k];
  }
  constexpr T fact(int n) const noexcept {
    if (n < 0)
      return 0;
    return fact_[n];
  }
  constexpr T inv(int n) const noexcept {
    if (n < 0)
      return 0;
    return inv_[n];
  }
  constexpr T finv(int n) const noexcept {
    if (n < 0)
      return 0;
    return finv_[n];
  }
  constexpr T perm(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[n - k];
  }
};

using mint = Fp<MOD2>;
BiCoef<mint> bc;
// using vec = vector<mint>;
// using mat = vector<vec>;

/*  ----------------------- AtCoder Library ---------------------------- */
// #include <atcoder/all>
// using namespace atcoder;
/*  ----------------------- AtCoder Library ---------------------------- */

void solve() {
  int N, K;
  cin >> N >> K;
  vector<int> L(N), R(N);
  REP(i, K) cin >> L[i] >> R[i];
  vector<mint> dp(N + 10), imos(N + 10);
  dp[0] = 1;
  REP(i, N) {
    if (i > 0)
      imos[i] += imos[i - 1];
    dp[i] += imos[i];
    REP(j, K) {
      int l = L[j] + i;
      int r = R[j] + i + 1;
      if (l < N)
        imos[l] += dp[i];
      if (r < N)
        imos[r] -= dp[i];
    }
  }
  cout << dp[N - 1] << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
  // int T; cin >> T; REP(t,T) solve();
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < n; i++)
#define ll long long
using namespace std;
typedef pair<int, int> P;
typedef pair<ll, ll> LP;
const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
const int INF = 1000000000;
const ll LINF = 1000000000000000000; // 1e18
const ll MOD = 1000000007;
const ll MOD2 = 998244353;
const double PI = acos(-1.0);
const double EPS = 1e-10;

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

/*  ----------------------- DEBUG FUNCTION ---------------------------- */
#define DUMPOUT cerr
void dump_function() { DUMPOUT << ' '; }
void dump_function(bool a) { DUMPOUT << a; }
void dump_function(int a) { DUMPOUT << a; }
void dump_function(long long a) { DUMPOUT << a; }
void dump_function(char a) { DUMPOUT << a; }
void dump_function(string &a) { DUMPOUT << a; }
void dump_function(double a) { DUMPOUT << a; }
template <class T> void dump_function(const vector<T> &);
template <class T, size_t size> void dump_function(const array<T, size> &);
template <class T, class L> void dump_function(const pair<T, L> &p);
template <class T, size_t size> void dump_function(const T (&)[size]);
template <class T> void dump_function(const vector<T> &a) {
  if (a.empty())
    return;
  dump_function(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    DUMPOUT << " ";
    dump_function(*i);
  }
  DUMPOUT << endl;
}
template <class T> void dump_function(const deque<T> &a) {
  if (a.empty())
    return;
  dump_function(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    DUMPOUT << " ";
    dump_function(*i);
  }
}
template <class T, size_t size> void dump_function(const array<T, size> &a) {
  dump_function(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    DUMPOUT << " ";
    dump_function(*i);
  }
}
template <class T, class L> void dump_function(const pair<T, L> &p) {
  DUMPOUT << '(';
  dump_function(p.first);
  DUMPOUT << ",";
  dump_function(p.second);
  DUMPOUT << ')';
}
template <class T> void dump_function(set<T> &x) {
  for (auto e : x)
    dump_function(e), DUMPOUT << " ";
  DUMPOUT << endl;
}
template <class T> void dump_function(multiset<T> &x) {
  for (auto e : x)
    dump_function(e), DUMPOUT << " ";
  DUMPOUT << endl;
}
template <class T, size_t size> void dump_function(const T (&a)[size]) {
  dump_function(a[0]);
  for (auto i = a; ++i != end(a);) {
    DUMPOUT << " ";
    dump_function(*i);
  }
}
template <class T> void dump_function(const T &a) { DUMPOUT << a; }
int dump_out() {
  DUMPOUT << '\\n';
  return 0;
}
template <class T> int dump_out(const T &t) {
  dump_function(t);
  DUMPOUT << '\\n';
  return 0;
}
template <class Head, class... Tail>
int dump_out(const Head &head, const Tail &...tail) {
  dump_function(head);
  DUMPOUT << ' ';
  dump_out(tail...);
  return 0;
}

#ifdef DEBUG_
#define dump(x)                                                                \\
  DUMPOUT << #x << ": ";                                                       \\
  dump_function(x);                                                            \\
  DUMPOUT << endl;
void dumps() {}
template <class T> void dumps(const T &t) {
  dump_function(t);
  DUMPOUT << " ";
}
template <class Head, class... Tail>
void dumps(const Head &head, const Tail &...tail) {
  dump_function(head);
  DUMPOUT << ' ';
  dump_out(tail...);
}
#else
#define dump(x)
template <class... T> void dumps(const T &...) {}
#endif
/*  ----------------------- DEBUG FUNCTION ---------------------------- */

template <int MOD> struct Fp {
  long long val;
  constexpr Fp(long long v = 0) noexcept : val(v % MOD) {
    if (val < 0)
      val += MOD;
  }
  constexpr int getmod() { return MOD; }
  constexpr Fp operator-() const noexcept { return val ? MOD - val : 0; }
  constexpr Fp operator+(const Fp &r) const noexcept { return Fp(*this) += r; }
  constexpr Fp operator-(const Fp &r) const noexcept { return Fp(*this) -= r; }
  constexpr Fp operator*(const Fp &r) const noexcept { return Fp(*this) *= r; }
  constexpr Fp operator/(const Fp &r) const noexcept { return Fp(*this) /= r; }
  constexpr Fp &operator+=(const Fp &r) noexcept {
    val += r.val;
    if (val >= MOD)
      val -= MOD;
    return *this;
  }
  constexpr Fp &operator-=(const Fp &r) noexcept {
    val -= r.val;
    if (val < 0)
      val += MOD;
    return *this;
  }
  constexpr Fp &operator*=(const Fp &r) noexcept {
    val = val * r.val % MOD;
    return *this;
  }
  constexpr Fp &operator/=(const Fp &r) noexcept {
    long long a = r.val, b = MOD, u = 1, v = 0;
    while (b) {
      long long t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    val = val * u % MOD;
    if (val < 0)
      val += MOD;
    return *this;
  }
  constexpr bool operator==(const Fp &r) const noexcept {
    return this->val == r.val;
  }
  constexpr bool operator!=(const Fp &r) const noexcept {
    return this->val != r.val;
  }
  friend constexpr ostream &operator<<(ostream &os, const Fp<MOD> &x) noexcept {
    return os << x.val;
  }
  friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, long long n) noexcept {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t = t * t;
    if (n & 1)
      t = t * a;
    return t;
  }
};

template <class T> struct BiCoef {
  vector<T> fact_, inv_, finv_;
  constexpr BiCoef() {}
  constexpr BiCoef(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
    init(n);
  }
  constexpr void init(int n) noexcept {
    fact_.assign(n, 1), inv_.assign(n, 1), finv_.assign(n, 1);
    int MOD = fact_[0].getmod();
    for (int i = 2; i < n; i++) {
      fact_[i] = fact_[i - 1] * i;
      inv_[i] = -inv_[MOD % i] * (MOD / i);
      finv_[i] = finv_[i - 1] * inv_[i];
    }
  }
  constexpr T com(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[k] * finv_[n - k];
  }
  constexpr T fact(int n) const noexcept {
    if (n < 0)
      return 0;
    return fact_[n];
  }
  constexpr T inv(int n) const noexcept {
    if (n < 0)
      return 0;
    return inv_[n];
  }
  constexpr T finv(int n) const noexcept {
    if (n < 0)
      return 0;
    return finv_[n];
  }
  constexpr T perm(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[n - k];
  }
};

using mint = Fp<MOD2>;
BiCoef<mint> bc;
// using vec = vector<mint>;
// using mat = vector<vec>;

/*  ----------------------- AtCoder Library ---------------------------- */
// #include <atcoder/all>
// using namespace atcoder;
/*  ----------------------- AtCoder Library ---------------------------- */

void solve() {
  int N, K;
  cin >> N >> K;
  vector<int> S;
  REP(i, K) {
    int L, R;
    cin >> L >> R;
    for (int i = L; i <= R; i++)
      S.emplace_back(i);
  }
  sort(S.begin(), S.end());
  vector<ll> dp(N + 10, -1);
  auto dfs = [&](auto &&self, int A) -> ll {
    if (A < 0)
      return 0;
    else if (A == 0)
      return 1;
    if (dp[A] >= 0)
      return dp[A];
    ll res = 0;
    for (auto x : S) {
      if (A - x < 0)
        break;
      res += self(self, A - x);
      res %= MOD2;
    }
    return dp[A] = res;
  };
  cout << dfs(dfs, N - 1) << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
  // int T; cin >> T; REP(t,T) solve();
}