Problem p02549 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define pli pair<ll, int>
#define pil pair<int, ll>
#define pll pair<ll, ll>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
#define endl '\n'
const int inf = 1000000007;
const ll INF = 1e18;
int mod = 998244353;
// int mod = 1000000007;
const double eps = 1e-8;
#define abs(x) (x >= 0 ? x : -(x))
#define lb(v, x) (int)(lower_bound(all(v), x) - v.begin())
#define ub(v, x) (int)(upper_bound(all(v), x) - v.begin())
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <typename T, typename U> T pow_(T a, U b) {
  return b ? pow_(a * a, b / 2) * (b % 2 ? a : 1) : 1;
}
ll modpow(ll a, ll b, ll _mod) {
  return b ? modpow(a * a % _mod, b / 2, _mod) * (b % 2 ? a : 1) % _mod : 1;
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.F << " " << p.S;
  return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  rep(i, sz(vec)) {
    if (i)
      os << " ";
    os << vec[i];
  }
  return os;
}
template <class T> ostream &operator<<(ostream &os, const set<T> &s) {
  for (auto si : s)
    os << si << " ";
  return os;
}
template <typename T> inline istream &operator>>(istream &is, vector<T> &v) {
  rep(j, sz(v)) is >> v[j];
  return is;
}
template <class T, class T2> inline void add(T &a, T2 b) {
  (a += (b % mod + mod)) %= mod;
}
template <class T> void operator+=(vector<T> &v, vector<T> v2) {
  rep(i, sz(v2)) v.eb(v2[i]);
}

void solve();

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(12);
  int T;
  T = 1;
  while (T--)
    solve();
}

struct mint {
  ll x;
  mint(ll x = 0) : x((mod + x % mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) { // コンストラクタの、modで割った余りがくる
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += -a.x + mod) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res += a; // ?
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const { // mint(a).pow(t) tは余りとったりしたらあかん
    if (t == 0)
      return 1;
    mint a = pow(t >> 1); // 再帰
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }
  // 逆元
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { // invを利用
    return (*this) *= a.inv();
  }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
  friend ostream &operator<<(ostream &s, mint a) { return s << a.x; }
};

void solve() {
  int n, k;
  cin >> n >> k;
  vector<pii> v(k);
  rep(i, k) cin >> v[i].F >> v[i].S;

  vector<mint> acc(n), dp(n);
  dp[0] = 1;

  rep(i, n) {
    if (i) {
      acc[i] += acc[i - 1];
      dp[i] = acc[i];
    }

    rep(j, k) {
      if (i + v[j].F >= n)
        continue;
      acc[i + v[j].F] += dp[i];
      acc[min(n - 1, i + v[j].S) + 1] -= dp[i];
    }
    // cerr << dp[i] << "  " << acc << endl;
  }
  cout << dp[n - 1] << endl;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define pli pair<ll, int>
#define pil pair<int, ll>
#define pll pair<ll, ll>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
#define endl '\n'
const int inf = 1000000007;
const ll INF = 1e18;
int mod = 998244353;
// int mod = 1000000007;
const double eps = 1e-8;
#define abs(x) (x >= 0 ? x : -(x))
#define lb(v, x) (int)(lower_bound(all(v), x) - v.begin())
#define ub(v, x) (int)(upper_bound(all(v), x) - v.begin())
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <typename T, typename U> T pow_(T a, U b) {
  return b ? pow_(a * a, b / 2) * (b % 2 ? a : 1) : 1;
}
ll modpow(ll a, ll b, ll _mod) {
  return b ? modpow(a * a % _mod, b / 2, _mod) * (b % 2 ? a : 1) % _mod : 1;
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.F << " " << p.S;
  return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  rep(i, sz(vec)) {
    if (i)
      os << " ";
    os << vec[i];
  }
  return os;
}
template <class T> ostream &operator<<(ostream &os, const set<T> &s) {
  for (auto si : s)
    os << si << " ";
  return os;
}
template <typename T> inline istream &operator>>(istream &is, vector<T> &v) {
  rep(j, sz(v)) is >> v[j];
  return is;
}
template <class T, class T2> inline void add(T &a, T2 b) {
  (a += (b % mod + mod)) %= mod;
}
template <class T> void operator+=(vector<T> &v, vector<T> v2) {
  rep(i, sz(v2)) v.eb(v2[i]);
}

void solve();

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(12);
  int T;
  T = 1;
  while (T--)
    solve();
}

struct mint {
  ll x;
  mint(ll x = 0) : x((mod + x % mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) { // コンストラクタの、modで割った余りがくる
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += -a.x + mod) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res += a; // ?
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const { // mint(a).pow(t) tは余りとったりしたらあかん
    if (t == 0)
      return 1;
    mint a = pow(t >> 1); // 再帰
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }
  // 逆元
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { // invを利用
    return (*this) *= a.inv();
  }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
  friend ostream &operator<<(ostream &s, mint a) { return s << a.x; }
};

void solve() {
  int n, k;
  cin >> n >> k;
  vector<pii> v(k);
  rep(i, k) cin >> v[i].F >> v[i].S;

  vector<mint> acc(n + 1), dp(n + 1);
  dp[0] = 1;

  rep(i, n) {
    if (i) {
      acc[i] += acc[i - 1];
      dp[i] = acc[i];
    }

    rep(j, k) {
      if (i + v[j].F >= n)
        continue;
      acc[i + v[j].F] += dp[i];
      acc[min(n - 1, i + v[j].S) + 1] -= dp[i];
    }
    // cerr << dp[i] << "  " << acc << endl;
  }
  cout << dp[n - 1] << endl;
}