Problem p02549 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>
using namespace std;

#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define RREP(i, n) for (int i = n - 1; i >= 0; i--)
#define FOR(i, k, n) for (int i = (k); i < (int)(n); i++)
#define all(i, n) (i), (i + n)

int dx4[4] = {1, 0, -1, 0};
int dy4[4] = {0, -1, 0, 1};
int dx8[8] = {1, 0, -1, 1, -1, 1, 0, -1};
int dy8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
int dx9[9] = {0, 1, 0, -1, 1, -1, 1, 0, -1};
int dy9[9] = {0, 1, 1, 1, 0, 0, -1, -1, -1};

typedef pair<int, int> P;
typedef pair<string, int> SP;
typedef long long ll;
typedef pair<ll, ll> PLL;

const int INF = 1e9;
const ll LLINF = 1e18;
const int MAX_V = 1e6 + 1;
// << fixed << setprecision
// --------------------------------------
int n, k;
const int mod = 998244353;
#include <cassert>
struct mint {
  ll x; // typedef long long ll;
  mint(ll 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(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  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, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

mint dp[20005];
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin >> n >> k;
  vector<PLL> vp;
  REP(i, k) {
    ll l, r;
    cin >> l >> r;

    vp.push_back(P(l, r));
  }

  dp[0] = 1;
  dp[1] = -1;
  mint sum = 0;
  REP(i, n) {
    sum += dp[i];
    dp[i] = sum;
    REP(j, k) {
      ll l = vp[j].first, r = vp[j].second;

      if (i + l <= n)
        dp[i + l] += dp[i];
      if (i + r + 1 <= n)
        dp[i + r + 1] -= dp[i];
    }
  }

  cout << dp[n - 1] << endl;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>
using namespace std;

#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define RREP(i, n) for (int i = n - 1; i >= 0; i--)
#define FOR(i, k, n) for (int i = (k); i < (int)(n); i++)
#define all(i, n) (i), (i + n)

int dx4[4] = {1, 0, -1, 0};
int dy4[4] = {0, -1, 0, 1};
int dx8[8] = {1, 0, -1, 1, -1, 1, 0, -1};
int dy8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
int dx9[9] = {0, 1, 0, -1, 1, -1, 1, 0, -1};
int dy9[9] = {0, 1, 1, 1, 0, 0, -1, -1, -1};

typedef pair<int, int> P;
typedef pair<string, int> SP;
typedef long long ll;
typedef pair<ll, ll> PLL;

const int INF = 1e9;
const ll LLINF = 1e18;
const int MAX_V = 1e6 + 1;
// << fixed << setprecision
// --------------------------------------
int n, k;
const int mod = 998244353;
#include <cassert>
struct mint {
  ll x; // typedef long long ll;
  mint(ll 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(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  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, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

mint dp[200005];
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin >> n >> k;
  vector<PLL> vp;
  REP(i, k) {
    ll l, r;
    cin >> l >> r;

    vp.push_back(P(l, r));
  }

  dp[0] = 1;
  dp[1] = -1;
  mint sum = 0;
  REP(i, n) {
    sum += dp[i];
    dp[i] = sum;
    REP(j, k) {
      ll l = vp[j].first, r = vp[j].second;

      if (i + l <= n)
        dp[i + l] += dp[i];
      if (i + r + 1 <= n)
        dp[i + r + 1] -= dp[i];
    }
  }

  cout << dp[n - 1] << endl;
}