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

/*
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@TT_beginner
*/

#include "bits/stdc++.h"
using namespace std;
#define ok1 cerr << "ok1\\n";
#define ok2 cerr << "ok2\\n";
#define M LLONG_MAX
#define rep(i, n) for (ll i = 0; i < n; ++i)
#define REP(i, s, n) for (ll i = (s); i < (n); ++i)
#define repr(i, n) for (ll i = n - 1; i >= 0; --i)
#define REPR(i, s, n) for (ll i = (s); i >= (n); --(i))
#define all(a) (a).begin(), (a).end()
#define reall(a) (a).rbegin(), (a).rend()
#define pb emplace_back // emplace_backの方が速いが使い慣れてないため
#define DOUBLE fixed << setprecision(15)
#define fi first
#define se second
#define mp make_pair
#define mt make_tuple
#define out(x, y) ((x) < 0 || h <= (x) || (y) < 0 || w <= (y))
#define TO_STRING(VariableName) #VariableName
#define debug(x) cerr << TO_STRING(x) << " is: " << x << " " << endl;
const double pi = acos(-1.0L);
typedef vector<int> vi;
typedef vector<string> vs;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef vector<char> vc;
typedef vector<double> vd;
typedef vector<bool> vb;
typedef deque<ll> dll;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> TLL;
typedef vector<P> vP;
typedef vector<TLL> vTLL;
// const ll mod = 1e9 + 7;
const ll mod = 998244353;
ll dx[8] = {-1, 0, 1, 0, 1, 1, -1, -1};
ll dy[8] = {0, -1, 0, 1, 1, -1, 1, -1};
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;
}
template <class A, class B>
ostream &operator<<(ostream &ost, const pair<A, B> &p) {
  ost << "{ " << p.first << ", " << p.second << " }";
  return ost;
}
template <class T> ostream &operator<<(ostream &ost, const vector<T> &v) {
  ost << "{ ";
  for (int i = 0; i < v.size(); i++) {
    if (i)
      ost << ", ";
    ost << v[i];
  }
  ost << " }";
  return ost;
}
template <class A, class B>
ostream &operator<<(ostream &ost, const map<A, B> &v) {
  ost << "{ ";
  for (auto p : v) {
    ost << "{ " << p.first << ", " << p.second << " }";
  }
  ost << " }";
  return ost;
}
void debugs() { std::cerr << "\\n"; }
template <class T, class... Args> void debugs(const T &x, const Args &...args) {
  std::cerr << x << " ";
  debugs(args...);
}
bool out_check(ll a, ll b) { return (0 <= a && a < b); }
double pitagoras(ll a, ll b, ll c, ll d) {
  double dx = a - b, dy = c - d;
  return pow(dx * dx + dy * dy, 0.5);
}
ll modpow(ll a, ll b, ll mo = mod) {
  ll c = 1;
  while (b > 0) {
    if (b & 1) {
      c = a * c % mo;
    }
    a = a * a % mo;
    b >>= 1;
  }
  return c;
}
void Yes(bool x) { cout << ((x) ? "Yes\\n" : "No\\n"); }
void YES(bool x) { cout << ((x) ? "YES\\n" : "NO\\n"); }
void yes(bool x) { cout << ((x) ? "yes\\n" : "no\\n"); }
void Yay(bool x) { cout << ((x) ? "Yay!\\n" : ":(\\n"); }
void OK(bool x) { cout << ((x) ? "OK!\\n" : "NG\\n"); }
//*
ll n, m, d, e, l, r, k, h, w, Q, ans, ret = M;
bool flag = false, flag2 = false, flag3 = false;
string s, t, u;
//*

/* For AtCoder Only
#include "atcoder/all"
using namespace atcoder;
//*/

int main() {
  // cin.tie(0); ios::sync_with_stdio(false);//not interactive
  cin >> n >> k;
  vP v;
  rep(i, k) {
    cin >> l >> r;
    v.push_back(P(l, r + 1));
  }
  vll dp(n);
  dp[0] = 1;
  dp[1] = -1;
  rep(i, n) {
    if (i > 0)
      (dp[i] += dp[i - 1]) %= mod;
    for (auto &p : v) {
      ll a, b;
      tie(a, b) = p;
      if (i + a < n)
        dp[i + a] += dp[i];
      if (i + b < n)
        dp[i + b] -= dp[i];
    }
  }
  cout << (dp[n - 1] + mod) % mod << endl;
}

Error: TLE

Fixed submission:

/*
vrrtll==???>;::::~~~~~~......`.`````````````````````...-?777!_.._?7u,~~~::::;>>??=lllttrrzu
rtll==??>>;::::~~~~......`.``````````````````
..J77!`````````...`..._T,~~~~:::;;>??==lttrrv
tll=??>>;:::~~~~......``````````````````..J7^ ` ``  ` ``
.,```````...._4,.~~~::;;>>?===lttr l=???>;;::~~~......`````HTSu,.``  `..J7!    `
`` .J"~N```````````..?&.~~~~::;;>>?==llt
=??>;;::~~~~.....``````.@????7SJ.?=     `     ` `` .J=....J;
``````````..h..~~~~::;;>??=ll
?>>;::~~~~.....````````.D?>>?>?>?8+.``         `.J"_......_b`
````````.S_.~~~~::;;>??=l
>;;::~~~~....``````````.C>??>>>?>>>?8J.`  ```..Y~..........J;  `  ` ```````
G...~~~~::;>??=
;;::~~~....```````` `..W1>>?>>>>?>>>>>?S,.`.7^.............-N``  `
``````` 6...~~~~::;>??
;:~~~~....``````` ..7` d??>>?>?>>?>>?>>1udMgggNNNNggJ.......([
`````.L...~~~~::;>?
:~~~.....`````` .7`   `K>?>?>>>>>>+ugNMMMB""7<!~~<?7TWMNNa,..w.`  ` `  `
`````,)....~~:::;>
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````(,...~~~~:;;
~~~....``` .7``   `    @?>>?1uMM#=.........................(TMNa......  `
``````4....~~~::;
~~~...`` .=`` `     `
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.... .=```  `` `
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~...v```` `
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(v_`,R_.............(NF..(/..(&,...`..........?MMMM;..................(MMs>>?1&T"!``....(1=
t..``
4,...........(N@....?,(NMNR_.....`..`....(WMM$..`....`..`..`....._HMe7=```````....~_1
...````.4,........-dM:.....(7MMMNR-.....................`............(.?^ ``
``````....~~~
...``````,4,....`.(NF........(MMMMb..`....--................`....(.7!        `
````....~~:
..````` ` `.5J_...JMt.........?NMMM[...`.HH5._(J7[...`...`...--?^`          `
`````....~~~:
...````` `  ` 7a,.dM{....`...../MMMN......(J=`  .>......._(/=             `  `
`````...~~~:
....```` ``     (4MN{..........._7"^...(/^    `.C....-(J=`                  ` `
```....~~~:
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`````....~~~::;;
~~j,..```````.D??>>>MM/....`........(-=`                          `  ` `
```````...~~~:::;>
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``````....~~~~::;??
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````````...~~~~:;;>??
::~~~?/....K??????>>?>dMN-_(7!                               `  ` `
````````....~~~:::>>??l
;:::~~/e.(K==?????????<dM"!                          `    `   ` ` ``
``````...~~~~:::;>??=l
@TT_beginner
*/

#include "bits/stdc++.h"
using namespace std;
#define ok1 cerr << "ok1\\n";
#define ok2 cerr << "ok2\\n";
#define M LLONG_MAX
#define rep(i, n) for (ll i = 0; i < n; ++i)
#define REP(i, s, n) for (ll i = (s); i < (n); ++i)
#define repr(i, n) for (ll i = n - 1; i >= 0; --i)
#define REPR(i, s, n) for (ll i = (s); i >= (n); --(i))
#define all(a) (a).begin(), (a).end()
#define reall(a) (a).rbegin(), (a).rend()
#define pb emplace_back // emplace_backの方が速いが使い慣れてないため
#define DOUBLE fixed << setprecision(15)
#define fi first
#define se second
#define mp make_pair
#define mt make_tuple
#define out(x, y) ((x) < 0 || h <= (x) || (y) < 0 || w <= (y))
#define TO_STRING(VariableName) #VariableName
#define debug(x) cerr << TO_STRING(x) << " is: " << x << " " << endl;
const double pi = acos(-1.0L);
typedef vector<int> vi;
typedef vector<string> vs;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef vector<char> vc;
typedef vector<double> vd;
typedef vector<bool> vb;
typedef deque<ll> dll;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> TLL;
typedef vector<P> vP;
typedef vector<TLL> vTLL;
// const ll mod = 1e9 + 7;
const ll mod = 998244353;
ll dx[8] = {-1, 0, 1, 0, 1, 1, -1, -1};
ll dy[8] = {0, -1, 0, 1, 1, -1, 1, -1};
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;
}
template <class A, class B>
ostream &operator<<(ostream &ost, const pair<A, B> &p) {
  ost << "{ " << p.first << ", " << p.second << " }";
  return ost;
}
template <class T> ostream &operator<<(ostream &ost, const vector<T> &v) {
  ost << "{ ";
  for (int i = 0; i < v.size(); i++) {
    if (i)
      ost << ", ";
    ost << v[i];
  }
  ost << " }";
  return ost;
}
template <class A, class B>
ostream &operator<<(ostream &ost, const map<A, B> &v) {
  ost << "{ ";
  for (auto p : v) {
    ost << "{ " << p.first << ", " << p.second << " }";
  }
  ost << " }";
  return ost;
}
void debugs() { std::cerr << "\\n"; }
template <class T, class... Args> void debugs(const T &x, const Args &...args) {
  std::cerr << x << " ";
  debugs(args...);
}
bool out_check(ll a, ll b) { return (0 <= a && a < b); }
double pitagoras(ll a, ll b, ll c, ll d) {
  double dx = a - b, dy = c - d;
  return pow(dx * dx + dy * dy, 0.5);
}
ll modpow(ll a, ll b, ll mo = mod) {
  ll c = 1;
  while (b > 0) {
    if (b & 1) {
      c = a * c % mo;
    }
    a = a * a % mo;
    b >>= 1;
  }
  return c;
}
void Yes(bool x) { cout << ((x) ? "Yes\\n" : "No\\n"); }
void YES(bool x) { cout << ((x) ? "YES\\n" : "NO\\n"); }
void yes(bool x) { cout << ((x) ? "yes\\n" : "no\\n"); }
void Yay(bool x) { cout << ((x) ? "Yay!\\n" : ":(\\n"); }
void OK(bool x) { cout << ((x) ? "OK!\\n" : "NG\\n"); }
//*
ll n, m, d, e, l, r, k, h, w, Q, ans, ret = M;
bool flag = false, flag2 = false, flag3 = false;
string s, t, u;
//*

/* For AtCoder Only
#include "atcoder/all"
using namespace atcoder;
//*/

int main() {
  // cin.tie(0); ios::sync_with_stdio(false);//not interactive
  cin >> n >> k;
  vP v;
  rep(i, k) {
    cin >> l >> r;
    v.push_back(P(l, r + 1));
  }
  sort(all(v));
  vll dp(n);
  dp[0] = 1;

  rep(i, n) {
    for (auto &p : v) {
      if (i - p.first < 0)
        continue;
      REP(d, p.first, p.second) {
        if (i - d < 0)
          continue;
        dp[i] += dp[i - d];
        dp[i] %= mod;
      }
    }
  }
  cout << dp[n - 1] % mod << endl;
}