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

// ######      ###      #######    #######    ##     #     #####        ###
// ##### // #     #    #   #          #        #       # #    #    #     # #   #
// ###  // #     #   #     #        #         #       #  #   #   #       #    #
// #    ###  //
// ######   #########      #          #       #   #  #   #           #########
// #   // #     #  #       #     #           #       #    # #   #    ####   # #
// #   // #     #  #       #    #            #       #     ##   #    #  #   # #
// //
// ######   #       #   #######    #######    #      #    #####  #   #       #
// #   //

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
#pragma GCC target("avx,avx2,fma")
#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double lld;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef pair<ll, ll> ppl;
#define ain(a, n)                                                              \\
  for (ll i = 0; i < (n); ++i)                                                 \\
    cin >> (a)[i];
#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
#define loop(i, n) for (ll i = 0; i < (n); ++i)
#define FOR(i, a, b) for (ll i = (a); i <= (b); ++i)
#define FORD(i, a, b) for (ll i = (a); i >= (b); --i)
#define cases                                                                  \\
  ll T = 0;                                                                    \\
  cin >> T;                                                                    \\
  while (T--)
#define ff first
#define ss second
#define all(v) v.begin(), v.end()
#define END "\\n"
#define pb push_back
#define mp make_pair
#define go(c, itr) for (auto itr = (c).begin(); itr != (c).end(); ++itr)
// #define back(c,itr) for(auto itr=(c).rbegin(); itr!=(c).rend(); ++itr)
#define PI 3.14159265359
#define inf 9e18
#define MOD 1000000007
#define MODU 998244353
#define fast                                                                   \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(NULL);                                                               \\
  cout.tie(NULL);
#define MAXN 300005
#define BLOCK 555
const string alpha = "abcdefghijklmnopqrstuvwxyz";
const ll N = 200005;
const long double epsilon = 1e-9;
inline ll myceil(ll a, ll b) { return (ceil(1.0 * a / b * 1.0)); }
ll binexp(ll a, ll b, ll m) {
  a %= m;
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a % m;
    a = a * a % m;
    b >>= 1;
  }
  return res;
}
ll modinvfermat(ll a, ll m) { return binexp(a, m - 2, m); }
void task(bool flag) {
  if (flag)
    cout << "YES\\n";
  else
    cout << "NO\\n";
}
ll lcm(ll a, ll b) { return ((1LL * a * b) / (__gcd(a, b))); }

signed main() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  fast ll n, k;
  cin >> n >> k;
  vector<ppl> range(k);
  loop(i, k) cin >> range[i].ff >> range[i].ss;

  vl dp(n + 1, 0), pref(n + 1, 0);
  pref[1] = 1, pref[2] = -1;
  FOR(i, 1, n) {
    (pref[i] += pref[i - 1] + dp[i]) %= MODU;
    (pref[i] += MODU) %= MODU;
    loop(j, k) {
      if (i + range[j].ff <= n)
        (dp[i + range[j].ff] += pref[i]) %= MODU;
      if (i + range[j].ss + 1 <= n) {
        (dp[i + range[j].ss + 1] -= pref[i]) %= MODU;
        (dp[i + range[j].ss + 1] += MODU) %= MODU;
      }
    }
  }

  cout << pref[n] << END;

#ifndef ONLINE_JUDGE
  cout << "\\nTime Elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " sec\\n";
#endif
  return 0;
}


Error: TLE

Fixed submission:

// ######      ###      #######    #######    ##     #     #####        ###
// ##### // #     #    #   #          #        #       # #    #    #     # #   #
// ###  // #     #   #     #        #         #       #  #   #   #       #    #
// #    ###  //
// ######   #########      #          #       #   #  #   #           #########
// #   // #     #  #       #     #           #       #    # #   #    ####   # #
// #   // #     #  #       #    #            #       #     ##   #    #  #   # #
// //
// ######   #       #   #######    #######    #      #    #####  #   #       #
// #   //

// #pragma GCC optimize(2)
// #pragma GCC optimize(3)
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
// #pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double lld;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef pair<ll, ll> ppl;
#define ain(a, n)                                                              \\
  for (ll i = 0; i < (n); ++i)                                                 \\
    cin >> (a)[i];
#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
#define loop(i, n) for (ll i = 0; i < (n); ++i)
#define FOR(i, a, b) for (ll i = (a); i <= (b); ++i)
#define FORD(i, a, b) for (ll i = (a); i >= (b); --i)
#define cases                                                                  \\
  ll T = 0;                                                                    \\
  cin >> T;                                                                    \\
  while (T--)
#define ff first
#define ss second
#define all(v) v.begin(), v.end()
#define END "\\n"
#define pb push_back
#define mp make_pair
#define go(c, itr) for (auto itr = (c).begin(); itr != (c).end(); ++itr)
// #define back(c,itr) for(auto itr=(c).rbegin(); itr!=(c).rend(); ++itr)
#define PI 3.14159265359
#define inf 9e18
#define MOD 1000000007
#define MODU 998244353
#define fast                                                                   \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(NULL);                                                               \\
  cout.tie(NULL);
#define MAXN 1000005
#define BLOCK 555
const string alpha = "abcdefghijklmnopqrstuvwxyz";
const ll N = 200005;
const long double epsilon = 1e-9;
inline ll myceil(ll a, ll b) {
  if (a % b == 0)
    return (a / b);
  return (a / b + 1);
}
ll spf[MAXN];
void sieve() {
  spf[1] = 1;
  for (ll i = 2; i < MAXN; i++)
    spf[i] = i;

  for (ll i = 4; i < MAXN; i += 2)
    spf[i] = 2;

  for (ll i = 3; i * i < MAXN; i++) {
    if (spf[i] == i) {
      for (ll j = i * i; j < MAXN; j += i)
        if (spf[j] == j)
          spf[j] = i;
    }
  }
}
inline ll binlen(ll n) {
  ll c = 0;
  while (n > 0)
    ++c, n /= 2;
  return c;
}
ll binexp(ll a, ll b, ll m) {
  a %= m;
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a % m;
    a = a * a % m;
    b >>= 1;
  }
  return res;
}
ll modinvfermat(ll a, ll m) { return binexp(a, m - 2, m); }
void task(bool flag) {
  if (flag)
    cout << "YES\\n";
  else
    cout << "NO\\n";
}
ll lcm(ll a, ll b) { return ((1LL * a * b) / (__gcd(a, b))); }

signed main() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  // fast
  ll n, k;
  scanf("%lld%lld", &n, &k);
  vl a;
  vector<ppl> lr(k);
  loop(i, k) { scanf("%lld%lld", &lr[i].ff, &lr[i].ss); }
  loop(i, k) {
    FOR(j, lr[i].ff, lr[i].ss) { a.pb(j); }
  }
  ll m = a.size();
  vl dp(n + 1, 0);
  dp[1] = 1;
  FOR(i, 1, n) {
    loop(j, m) {
      if (i - a[j] < 0)
        continue;
      (dp[i] += dp[i - a[j]]) %= MODU;
    }
  }
  printf("%lld\\n", dp[n]);

  // #ifndef ONLINE_JUDGE
  //     cout << "\\nTime Elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << "
  //     sec\\n";
  // #endif
  return 0;
}