Problem p02549 (C++)

Buggy submission (status: Runtime Error):
// بساملہ ہیر رحمن نیر رحیم
//---------------------------//
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")
#include <algorithm>
#include <bitset>
#include <chrono>
#include <climits>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
// #define PBDS tree<long long int,null_type,less<long long int>,
// rb_tree_tag,tree_order_statistics_node_update> using namespace __gnu_pbds;
#define arrsize 100001
#define dpsize 1001
#define vpp vector<PP>
#define vll vector<ll>
#define vcc vector<char>
#define endl "\n"
#define vbb vector<bool>
#define w(t) while (t--)
#define PP pair<ll, ll>
#define test(x)                                                                \
  ll t;                                                                        \
  cin >> t;                                                                    \
  w(t) x()
#define __lb lower_bound
#define __ub upper_bound
#define szs(x) x.length()
#define szv(x) x.size()
#define INF 1999999996000000010
#define ll long long int
#define takeINP(arr, n)                                                        \
  for (long long int i = 0; i < n; i++)                                        \
    cin >> arr[i];
#define f(i, s, e) for (long long int i = s; i < e; i++)
#define cf(i, s, e) for (long long int i = s; i <= e; i++)
#define rf(i, e, s) for (long long int i = e - 1; i >= s; i--)
#define mem(arr) memset(arr, 0, sizeof(arr));
#define MOD 998244353
#define rsz(x, n) x.resize(n)
#define rsr(x, n) x.reserve(n)
#define mp(a, b) make_pair(a, b)
#define pb push_back
#define print(arr, s, e)                                                       \
  f(i, s, e) cout << arr[i] << " ";                                            \
  cout << endl;
#define all(v) v.begin(), v.end()
#define ff first
#define ss second
#define vll vector<ll>
#define triplet pair<ll, pair<ll, ll>>
#define MITR(a, b) map<a, b>::reverse_iterator
using namespace std;
using namespace chrono;

///---------------Functions---------------------///
ll advceil(ll num, ll den) {
  return (num % den == 0 ? num / den : num / den + 1);
}
ll lstbt(ll val) {
  ll msk = val & (val - 1);
  return log2(val ^ msk);
}
ll modexpo(ll a, ll b) {
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = (res % MOD * a % MOD) % MOD;
    a = (a % MOD * a % MOD);
    b /= 2;
  }
  return res;
}
ll expo(ll a, ll b) {
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = (res * a);
    a = (a * a);
    b /= 2;
  }
  return res;
}
ll gcd(ll a, ll b) { return a == 0 ? b : gcd(b % a, a); }
vll CALCfactor(ll n) {
  vll factor(n + 2, 0);
  for (ll i = 4; i <= n; i += 2)
    factor[i] = 2;
  for (ll j = 3; j <= n; j += 2) {
    if (factor[j])
      continue;
    for (ll i = 2 * j; i <= n; i += j)
      factor[i] = j;
  }
  return factor;
}
vll CALCprimeNUM(ll n) {
  vll factor = CALCfactor(n);
  vll primeNUM;
  primeNUM.reserve(n + 2);
  cf(i, 2, n) if (!factor[i]) primeNUM.pb(i);
  return primeNUM;
}
vll CALCprimeFACTOR(ll n) {
  vll factor = CALCfactor(n);
  vll ans;
  while (factor[n] != 0) {
    ans.pb(factor[n]);
    n /= factor[n];
  }
  ans.pb(n);
  return ans;
}
vll unique(vll x) {
  sort(all(x));
  set<ll> s;
  vll ans;
  ans.reserve(szv(x));
  for (auto elem : x)
    s.insert(elem);
  for (auto elem : s)
    ans.pb(elem);
  return ans;
}
vll ZALGO(string s, string pat) {
  ll lens = szs(pat);
  pat += char(36);
  pat += s;
  s = pat;
  vll pref(szs(s) + 1, 0);
  pref[0] = szs(s);
  ll spt = -1;
  ll ept = -1;
  ll processCnt = 0;
  for (ll i = 1; i < szs(s); i++) {
    bool isdone = false;
    if (i <= ept and i >= spt) {
      if (pref[i - spt] + i <= ept)
        pref[i] = pref[i - spt], isdone = true;
      processCnt++;
    }
    if (!isdone) {
      ll ptr = i;
      ll lo = 0;
      while (s[lo] == s[ptr])
        ptr++, lo++, processCnt++;
      if (ept < ptr - 1) {
        spt = i;
        ept = ptr - 1;
      }
      pref[i] = lo;
    }
  }
  vll ans;
  ans.reserve(szs(s) - lens);
  for (ll i = lens + 1; i < szs(s); i++)
    ans.pb(pref[i]);
  return ans;
}
void spclSort(vector<pair<pair<ll, ll>, ll>> &v) {
  ll n = szv(v);
  {
    vll cnt(n);
    for (auto elem : v) {
      cnt[elem.ff.ss]++;
    }
    vector<pair<pair<ll, ll>, ll>> a_new(n);
    vll pos(szv(cnt));
    pos[0] = 0;
    for (ll i = 1; i < szv(cnt); i++) {
      pos[i] = cnt[i - 1] + pos[i - 1];
    }
    for (auto elem : v) {
      a_new[pos[elem.ff.ss]] = elem;
      pos[elem.ff.ss]++;
    }
    v = a_new;
  }
  {
    vll cnt(n, 0);
    for (auto elem : v) {
      cnt[elem.ff.ff]++;
    }
    vector<pair<pair<ll, ll>, ll>> a_new(n);
    vll pos(szv(cnt));
    pos[0] = 0;
    for (ll i = 1; i < szv(cnt); i++) {
      pos[i] = cnt[i - 1] + pos[i - 1];
    }
    for (auto elem : v) {
      a_new[pos[elem.ff.ff]] = elem;
      pos[elem.ff.ff]++;
    }
    v = a_new;
  }
}
pair<vector<vll>, vector<vll>> getOrdering(string s) {
  s += char(36);
  vector<vll> dp;
  dp.reserve(log2(szs(s)) + 3);
  vector<vll> dp2;
  dp2.reserve(log2(szs(s)) + 3);
  vll ordering(szs(s)), eqClass(szs(s));
  {
    vector<pair<char, ll>> temp(szs(s));
    f(i, 0, szs(s)) temp[i] = {s[i], i};
    sort(all(temp));
    f(i, 0, szv(temp)) ordering[temp[i].ss] = i;
    eqClass[temp[0].ss] = 0;
    f(i, 1, szv(temp)) {
      if (temp[i].ff != temp[i - 1].ff)
        eqClass[temp[i].ss] = eqClass[temp[i - 1].ss] + 1;
      else
        eqClass[temp[i].ss] = eqClass[temp[i - 1].ss];
    }
    dp.pb(ordering);
    dp2.pb(eqClass);
  }
  ll k = 1;
  while ((1 << (k - 1)) < szs(s)) {
    vector<pair<pair<ll, ll>, ll>> arr(szs(s));
    for (ll i = 0; i < szs(s); i++) {
      arr[i] = {{eqClass[i], eqClass[(i + (1 << (k - 1))) % szs(s)]}, i};
    }
    spclSort(arr);
    f(i, 0, szs(s)) ordering[arr[i].ss] = i;
    eqClass[arr[0].ss] = 0;
    f(i, 1, szv(s)) {
      if (arr[i].ff != arr[i - 1].ff)
        eqClass[arr[i].ss] = eqClass[arr[i - 1].ss] + 1;
      else
        eqClass[arr[i].ss] = eqClass[arr[i - 1].ss];
    }
    dp.pb(ordering);
    dp2.pb(eqClass);
    k++;
  }
  return {dp, dp2};
}
vll sortOrdering(vector<vll> dp) {
  vll arr = dp[szv(dp) - 1];
  vll ans(szv(arr));
  ll cnt = 0;
  for (auto elem : arr) {
    ans[elem] = cnt;
    cnt++;
  }
  return ans;
}
vll getLps(string pat) {
  ll i = 1;
  ll j = 0;
  vll lps(szs(pat), 0);
  lps[0] = 0;
  while (i < szs(pat)) {
    if (pat[i] == pat[j])
      lps[i] = j + 1, i++, j++;
    else if (j == 0)
      lps[i] = 0, i++;
    else
      j = lps[j - 1];
  }
  return lps;
}
///---------x------------x----------x-----------///
ll BIT[arrsize] = {};
ll n;
void update(ll idx, ll val) {
  for (ll i = idx; i <= n; i += (i & (-i)))
    BIT[i] += val, BIT[i] %= MOD;
}
ll query(ll idx) {
  ll sum = 0;
  for (ll i = idx; i > 0; i -= (i & (-i)))
    sum += BIT[i], sum %= MOD;
  return sum;
}
ll get(ll l, ll r) {
  if (l > r or l < 1 or r > n)
    return 0;
  return (query(r) - query(l - 1) + MOD) % MOD;
}

void solve() {
  ll k;
  cin >> n >> k;
  vpp arr(k);
  f(i, 0, k) cin >> arr[i].ff >> arr[i].ss;

  update(1, 1);
  cf(i, 2, n) {
    ll cnt = 0;
    f(j, 0, k) {
      ll lo = i - arr[j].ff;
      ll hi = i - arr[j].ss;
      if (lo < 1)
        continue;
      if (hi < 1)
        hi = i - min(arr[j].ss, i - 1);
      cnt += (get(hi, lo));
      cnt %= MOD;
    }
    update(i, cnt);
    // cout<<"#"<<i<<" "<<cnt<<endl;
  }

  cout << get(n, n) << endl;
}

int main() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  auto start1 = high_resolution_clock::now();
  solve();
  // test(solve);
  auto stop1 = high_resolution_clock::now();
  auto duration = duration_cast<microseconds>(stop1 - start1);
#ifndef ONLINE_JUDGE
  cerr << "Time: " << duration.count() / 1000.0 << endl;
  cout << duration.count() / 1000.0 << endl;
#endif
}

Fixed submission:
// بساملہ ہیر رحمن نیر رحیم
//---------------------------//
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")
#include <algorithm>
#include <bitset>
#include <chrono>
#include <climits>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
// #define PBDS tree<long long int,null_type,less<long long int>,
// rb_tree_tag,tree_order_statistics_node_update> using namespace __gnu_pbds;
#define arrsize 2000001
#define dpsize 1001
#define vpp vector<PP>
#define vll vector<ll>
#define vcc vector<char>
#define endl "\n"
#define vbb vector<bool>
#define w(t) while (t--)
#define PP pair<ll, ll>
#define test(x)                                                                \
  ll t;                                                                        \
  cin >> t;                                                                    \
  w(t) x()
#define __lb lower_bound
#define __ub upper_bound
#define szs(x) x.length()
#define szv(x) x.size()
#define INF 1999999996000000010
#define ll long long int
#define takeINP(arr, n)                                                        \
  for (long long int i = 0; i < n; i++)                                        \
    cin >> arr[i];
#define f(i, s, e) for (long long int i = s; i < e; i++)
#define cf(i, s, e) for (long long int i = s; i <= e; i++)
#define rf(i, e, s) for (long long int i = e - 1; i >= s; i--)
#define mem(arr) memset(arr, 0, sizeof(arr));
#define MOD 998244353
#define rsz(x, n) x.resize(n)
#define rsr(x, n) x.reserve(n)
#define mp(a, b) make_pair(a, b)
#define pb push_back
#define print(arr, s, e)                                                       \
  f(i, s, e) cout << arr[i] << " ";                                            \
  cout << endl;
#define all(v) v.begin(), v.end()
#define ff first
#define ss second
#define vll vector<ll>
#define triplet pair<ll, pair<ll, ll>>
#define MITR(a, b) map<a, b>::reverse_iterator
using namespace std;
using namespace chrono;

///---------------Functions---------------------///
ll advceil(ll num, ll den) {
  return (num % den == 0 ? num / den : num / den + 1);
}
ll lstbt(ll val) {
  ll msk = val & (val - 1);
  return log2(val ^ msk);
}
ll modexpo(ll a, ll b) {
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = (res % MOD * a % MOD) % MOD;
    a = (a % MOD * a % MOD);
    b /= 2;
  }
  return res;
}
ll expo(ll a, ll b) {
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = (res * a);
    a = (a * a);
    b /= 2;
  }
  return res;
}
ll gcd(ll a, ll b) { return a == 0 ? b : gcd(b % a, a); }
vll CALCfactor(ll n) {
  vll factor(n + 2, 0);
  for (ll i = 4; i <= n; i += 2)
    factor[i] = 2;
  for (ll j = 3; j <= n; j += 2) {
    if (factor[j])
      continue;
    for (ll i = 2 * j; i <= n; i += j)
      factor[i] = j;
  }
  return factor;
}
vll CALCprimeNUM(ll n) {
  vll factor = CALCfactor(n);
  vll primeNUM;
  primeNUM.reserve(n + 2);
  cf(i, 2, n) if (!factor[i]) primeNUM.pb(i);
  return primeNUM;
}
vll CALCprimeFACTOR(ll n) {
  vll factor = CALCfactor(n);
  vll ans;
  while (factor[n] != 0) {
    ans.pb(factor[n]);
    n /= factor[n];
  }
  ans.pb(n);
  return ans;
}
vll unique(vll x) {
  sort(all(x));
  set<ll> s;
  vll ans;
  ans.reserve(szv(x));
  for (auto elem : x)
    s.insert(elem);
  for (auto elem : s)
    ans.pb(elem);
  return ans;
}
vll ZALGO(string s, string pat) {
  ll lens = szs(pat);
  pat += char(36);
  pat += s;
  s = pat;
  vll pref(szs(s) + 1, 0);
  pref[0] = szs(s);
  ll spt = -1;
  ll ept = -1;
  ll processCnt = 0;
  for (ll i = 1; i < szs(s); i++) {
    bool isdone = false;
    if (i <= ept and i >= spt) {
      if (pref[i - spt] + i <= ept)
        pref[i] = pref[i - spt], isdone = true;
      processCnt++;
    }
    if (!isdone) {
      ll ptr = i;
      ll lo = 0;
      while (s[lo] == s[ptr])
        ptr++, lo++, processCnt++;
      if (ept < ptr - 1) {
        spt = i;
        ept = ptr - 1;
      }
      pref[i] = lo;
    }
  }
  vll ans;
  ans.reserve(szs(s) - lens);
  for (ll i = lens + 1; i < szs(s); i++)
    ans.pb(pref[i]);
  return ans;
}
void spclSort(vector<pair<pair<ll, ll>, ll>> &v) {
  ll n = szv(v);
  {
    vll cnt(n);
    for (auto elem : v) {
      cnt[elem.ff.ss]++;
    }
    vector<pair<pair<ll, ll>, ll>> a_new(n);
    vll pos(szv(cnt));
    pos[0] = 0;
    for (ll i = 1; i < szv(cnt); i++) {
      pos[i] = cnt[i - 1] + pos[i - 1];
    }
    for (auto elem : v) {
      a_new[pos[elem.ff.ss]] = elem;
      pos[elem.ff.ss]++;
    }
    v = a_new;
  }
  {
    vll cnt(n, 0);
    for (auto elem : v) {
      cnt[elem.ff.ff]++;
    }
    vector<pair<pair<ll, ll>, ll>> a_new(n);
    vll pos(szv(cnt));
    pos[0] = 0;
    for (ll i = 1; i < szv(cnt); i++) {
      pos[i] = cnt[i - 1] + pos[i - 1];
    }
    for (auto elem : v) {
      a_new[pos[elem.ff.ff]] = elem;
      pos[elem.ff.ff]++;
    }
    v = a_new;
  }
}
pair<vector<vll>, vector<vll>> getOrdering(string s) {
  s += char(36);
  vector<vll> dp;
  dp.reserve(log2(szs(s)) + 3);
  vector<vll> dp2;
  dp2.reserve(log2(szs(s)) + 3);
  vll ordering(szs(s)), eqClass(szs(s));
  {
    vector<pair<char, ll>> temp(szs(s));
    f(i, 0, szs(s)) temp[i] = {s[i], i};
    sort(all(temp));
    f(i, 0, szv(temp)) ordering[temp[i].ss] = i;
    eqClass[temp[0].ss] = 0;
    f(i, 1, szv(temp)) {
      if (temp[i].ff != temp[i - 1].ff)
        eqClass[temp[i].ss] = eqClass[temp[i - 1].ss] + 1;
      else
        eqClass[temp[i].ss] = eqClass[temp[i - 1].ss];
    }
    dp.pb(ordering);
    dp2.pb(eqClass);
  }
  ll k = 1;
  while ((1 << (k - 1)) < szs(s)) {
    vector<pair<pair<ll, ll>, ll>> arr(szs(s));
    for (ll i = 0; i < szs(s); i++) {
      arr[i] = {{eqClass[i], eqClass[(i + (1 << (k - 1))) % szs(s)]}, i};
    }
    spclSort(arr);
    f(i, 0, szs(s)) ordering[arr[i].ss] = i;
    eqClass[arr[0].ss] = 0;
    f(i, 1, szv(s)) {
      if (arr[i].ff != arr[i - 1].ff)
        eqClass[arr[i].ss] = eqClass[arr[i - 1].ss] + 1;
      else
        eqClass[arr[i].ss] = eqClass[arr[i - 1].ss];
    }
    dp.pb(ordering);
    dp2.pb(eqClass);
    k++;
  }
  return {dp, dp2};
}
vll sortOrdering(vector<vll> dp) {
  vll arr = dp[szv(dp) - 1];
  vll ans(szv(arr));
  ll cnt = 0;
  for (auto elem : arr) {
    ans[elem] = cnt;
    cnt++;
  }
  return ans;
}
vll getLps(string pat) {
  ll i = 1;
  ll j = 0;
  vll lps(szs(pat), 0);
  lps[0] = 0;
  while (i < szs(pat)) {
    if (pat[i] == pat[j])
      lps[i] = j + 1, i++, j++;
    else if (j == 0)
      lps[i] = 0, i++;
    else
      j = lps[j - 1];
  }
  return lps;
}
///---------x------------x----------x-----------///
ll BIT[arrsize] = {};
ll n;
void update(ll idx, ll val) {
  for (ll i = idx; i <= n; i += (i & (-i)))
    BIT[i] += val, BIT[i] %= MOD;
}
ll query(ll idx) {
  ll sum = 0;
  for (ll i = idx; i > 0; i -= (i & (-i)))
    sum += BIT[i], sum %= MOD;
  return sum;
}
ll get(ll l, ll r) {
  if (l > r or l < 1 or r > n)
    return 0;
  return (query(r) - query(l - 1) + MOD) % MOD;
}

void solve() {
  ll k;
  cin >> n >> k;
  vpp arr(k);
  f(i, 0, k) cin >> arr[i].ff >> arr[i].ss;

  update(1, 1);
  cf(i, 2, n) {
    ll cnt = 0;
    f(j, 0, k) {
      ll lo = i - arr[j].ff;
      ll hi = i - arr[j].ss;
      if (lo < 1)
        continue;
      if (hi < 1)
        hi = i - min(arr[j].ss, i - 1);
      cnt += (get(hi, lo));
      cnt %= MOD;
    }
    update(i, cnt);
    // cout<<"#"<<i<<" "<<cnt<<endl;
  }

  cout << get(n, n) << endl;
}

int main() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  auto start1 = high_resolution_clock::now();
  solve();
  // test(solve);
  auto stop1 = high_resolution_clock::now();
  auto duration = duration_cast<microseconds>(stop1 - start1);
#ifndef ONLINE_JUDGE
  cerr << "Time: " << duration.count() / 1000.0 << endl;
  cout << duration.count() / 1000.0 << endl;
#endif
}