Problem p02549 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double lf;
typedef pair<int, int> ii;
typedef pair<ii, int> iii;
#define REP(i, n) for (int i = 0; i < n; i++)
#define REP1(i, n) for (int i = 1; i <= n; i++)
#define RST(i, n) memset(i, n, sizeof i)
#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define X first
#define Y second
#define eb emplace_back
#ifdef cold66
#define debug(...)                                                             \
  do {                                                                         \
    fprintf(stderr, "LINE %d: (%s) = ", __LINE__, #__VA_ARGS__);               \
    _do(__VA_ARGS__);                                                          \
  } while (0)
template <typename T> void _do(T &&_x) { cerr << _x << endl; }
template <typename T, typename... S> void _do(T &&_x, S &&..._t) {
  cerr << _x << ", ";
  _do(_t...);
}
template <typename _a, typename _b>
ostream &operator<<(ostream &_s, const pair<_a, _b> &_p) {
  return _s << "(" << _p.X << "," << _p.Y << ")";
}
template <typename It> ostream &_OUTC(ostream &_s, It _ita, It _itb) {
  _s << "{";
  for (It _it = _ita; _it != _itb; _it++) {
    _s << (_it == _ita ? "" : ",") << *_it;
  }
  _s << "}";
  return _s;
}
template <typename _a> ostream &operator<<(ostream &_s, vector<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a> ostream &operator<<(ostream &_s, set<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a, typename _b>
ostream &operator<<(ostream &_s, map<_a, _b> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _t> void pary(_t _a, _t _b) {
  _OUTC(cerr, _a, _b);
  cerr << endl;
}
#define IOS()
#else
#define debug(...)
#define pary(...)
#define endl '\n'
#define IOS()                                                                  \
  ios_base::sync_with_stdio(0);                                                \
  cin.tie(0);
#endif // cold66
//}
template <class T> inline bool chkmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T> inline bool chkmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}

const ll MAXn = 1e5 + 5, MAXlg = __lg(MAXn) + 2;
const ll MOD = 998244353;
const ll INF = 0x3f3f3f3f;

ll dp[MAXn], sum[MAXn];
ii d[MAXn];
ll add(ll x, ll y) {
  ll ret = x + y;
  if (ret >= MOD)
    ret -= MOD;
  return ret;
}
ll sub(ll a, ll b) {
  ll ret = a - b;
  if (ret < 0)
    ret += MOD;
  return ret;
}
int main() {
  IOS();
  ll n, k;
  cin >> n >> k;
  for (int i = 0; i < k; ++i) {
    cin >> d[i].X >> d[i].Y;
  }
  sort(d, d + k);

  dp[1] = 1;
  sum[1] = 1;
  for (int i = 2; i <= n; ++i)
    sum[i] = 1;
  for (ll i = 2; i <= n; ++i) {
    for (ll j = 0; j < k; ++j) {
      debug(i);
      ll r = i - d[j].X, l = max(0LL, i - d[j].Y - 1);
      if (r < 0)
        break;
      debug(l, r);
      dp[i] = add(dp[i], sub(sum[r], sum[l]));
    }
    sum[i] = add(sum[i - 1], dp[i]);
  }
  cout << dp[n] << endl;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double lf;
typedef pair<int, int> ii;
typedef pair<ii, int> iii;
#define REP(i, n) for (int i = 0; i < n; i++)
#define REP1(i, n) for (int i = 1; i <= n; i++)
#define RST(i, n) memset(i, n, sizeof i)
#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define X first
#define Y second
#define eb emplace_back
#ifdef cold66
#define debug(...)                                                             \
  do {                                                                         \
    fprintf(stderr, "LINE %d: (%s) = ", __LINE__, #__VA_ARGS__);               \
    _do(__VA_ARGS__);                                                          \
  } while (0)
template <typename T> void _do(T &&_x) { cerr << _x << endl; }
template <typename T, typename... S> void _do(T &&_x, S &&..._t) {
  cerr << _x << ", ";
  _do(_t...);
}
template <typename _a, typename _b>
ostream &operator<<(ostream &_s, const pair<_a, _b> &_p) {
  return _s << "(" << _p.X << "," << _p.Y << ")";
}
template <typename It> ostream &_OUTC(ostream &_s, It _ita, It _itb) {
  _s << "{";
  for (It _it = _ita; _it != _itb; _it++) {
    _s << (_it == _ita ? "" : ",") << *_it;
  }
  _s << "}";
  return _s;
}
template <typename _a> ostream &operator<<(ostream &_s, vector<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a> ostream &operator<<(ostream &_s, set<_a> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _a, typename _b>
ostream &operator<<(ostream &_s, map<_a, _b> &_c) {
  return _OUTC(_s, ALL(_c));
}
template <typename _t> void pary(_t _a, _t _b) {
  _OUTC(cerr, _a, _b);
  cerr << endl;
}
#define IOS()
#else
#define debug(...)
#define pary(...)
#define endl '\n'
#define IOS()                                                                  \
  ios_base::sync_with_stdio(0);                                                \
  cin.tie(0);
#endif // cold66
//}
template <class T> inline bool chkmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T> inline bool chkmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}

const ll MAXn = 2e5 + 5, MAXlg = __lg(MAXn) + 2;
const ll MOD = 998244353;
const ll INF = 0x3f3f3f3f;

ll dp[MAXn], sum[MAXn];
ii d[MAXn];
ll add(ll x, ll y) {
  ll ret = x + y;
  if (ret >= MOD)
    ret -= MOD;
  return ret;
}
ll sub(ll a, ll b) {
  ll ret = a - b;
  if (ret < 0)
    ret += MOD;
  return ret;
}
int main() {
  IOS();
  ll n, k;
  cin >> n >> k;
  for (int i = 0; i < k; ++i) {
    cin >> d[i].X >> d[i].Y;
  }
  sort(d, d + k);

  dp[1] = 1;
  sum[1] = 1;
  for (int i = 2; i <= n; ++i)
    sum[i] = 1;
  for (ll i = 2; i <= n; ++i) {
    for (ll j = 0; j < k; ++j) {
      debug(i);
      ll r = i - d[j].X, l = max(0LL, i - d[j].Y - 1);
      if (r < 0)
        break;
      debug(l, r);
      dp[i] = add(dp[i], sub(sum[r], sum[l]));
    }
    sum[i] = add(sum[i - 1], dp[i]);
  }
  cout << dp[n] << endl;
}