Problem p02554 (C++) — buggy submission, verdict: Time Limit Exceeded

// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("avx2")
//  293206GT
#include <algorithm>
#include <algorithm>
#include <bitset>
#include <chrono>
#include <cmath>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

typedef long long ll;
#define int ll
using namespace std;
#define put(a) cout << (a) << '\\n'
#define sqr(x) (x) * (x)
typedef pair<int, int> pii;
typedef long double ld;
typedef pair<ld, ld> pld;
typedef unsigned long long ull;

typedef vector<int> vi;
typedef vector<pii> vpii;
#define rep(x, y, a) for (int x = (y); x < (int)(a); ++x)
#define all(a) a.begin(), a.end()
#define chkmax(a, b) a = max(a, (b))
#define chkmin(a, b) a = min(a, (b))
#define prev asasdasd
#define next aasdasda
#define left asdasdasdasd
#define right asnabsdkasdl
#define rank asdasdknlasd
#define move asdasdas

namespace IO {

template <class A, class B>
ostream &operator<<(ostream &out, vector<pair<A, B>> a);

template <class A> ostream &operator<<(ostream &out, vector<A> a);

template <class A, class B> ostream &operator<<(ostream &out, pair<A, B> a) {
  out << a.first << " " << a.second;
  return out;
}

template <class A, class B>
ostream &operator<<(ostream &out, vector<pair<A, B>> a) {
  for (pair<A, B> x : a)
    out << x.first << " " << x.second << '\\n';
  return out;
}

template <class A> ostream &operator<<(ostream &out, vector<A> a) {
  for (A x : a)
    out << x << ' ';
  return out;
}

template <class A, class B> istream &operator>>(istream &in, pair<A, B> &a) {
  in >> a.first >> a.second;
  return in;
}

template <class A> istream &operator>>(istream &in, vector<A> &a) {
  for (A &x : a)
    in >> x;
  return in;
}
} // namespace IO
using namespace IO;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int bp(int a, int b, int m) {
  if (b == 0)
    return 1;
  int x = bp(a, b / 2, m);
  x = x * x % m;
  x *= max(1ll, (b % 2) * a);
  return x % m;
}
void solve() {
  int n;
  cin >> n;
  int M = 1e9 + 7;
  int ans = bp(10, n, M);
  vi fact(n + 1);
  vi rfact(n + 1);
  fact[0] = 1;
  rep(i, 1, n + 1) fact[i] = fact[i - 1] * i % M;
  rep(i, 1, n + 1) rfact[i] = bp(fact[i], M - 2, M);
  rep(i, 1, n) {
    ans -= bp(8, n - i, M) * fact[n] % M * rfact[i] % M * rfact[n - i] % M * 2;
    ans = (ans % M + M) % M;
  }
  ans -= bp(8, n, M);
  ans -= 2;
  put((ans + M * 10) % M);
}

signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout.precision(30);
  //    freopen("input.txt", "r", stdin);
  int q = 1;
  //    cin >> q;

  while (q--)
    solve();
}


Error: TLE

Fixed submission:

// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("avx2")
//  293206GT
#include <algorithm>
#include <algorithm>
#include <bitset>
#include <chrono>
#include <cmath>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

typedef long long ll;
#define int ll
using namespace std;
#define put(a) cout << (a) << '\\n'
#define sqr(x) (x) * (x)
typedef pair<int, int> pii;
typedef long double ld;
typedef pair<ld, ld> pld;
typedef unsigned long long ull;

typedef vector<int> vi;
typedef vector<pii> vpii;
#define rep(x, y, a) for (int x = (y); x < (int)(a); ++x)
#define all(a) a.begin(), a.end()
#define chkmax(a, b) a = max(a, (b))
#define chkmin(a, b) a = min(a, (b))
#define prev asasdasd
#define next aasdasda
#define left asdasdasdasd
#define right asnabsdkasdl
#define rank asdasdknlasd
#define move asdasdas

namespace IO {

template <class A, class B>
ostream &operator<<(ostream &out, vector<pair<A, B>> a);

template <class A> ostream &operator<<(ostream &out, vector<A> a);

template <class A, class B> ostream &operator<<(ostream &out, pair<A, B> a) {
  out << a.first << " " << a.second;
  return out;
}

template <class A, class B>
ostream &operator<<(ostream &out, vector<pair<A, B>> a) {
  for (pair<A, B> x : a)
    out << x.first << " " << x.second << '\\n';
  return out;
}

template <class A> ostream &operator<<(ostream &out, vector<A> a) {
  for (A x : a)
    out << x << ' ';
  return out;
}

template <class A, class B> istream &operator>>(istream &in, pair<A, B> &a) {
  in >> a.first >> a.second;
  return in;
}

template <class A> istream &operator>>(istream &in, vector<A> &a) {
  for (A &x : a)
    in >> x;
  return in;
}
} // namespace IO
using namespace IO;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int bp(int a, int b, int m) {
  if (b == 0)
    return 1;
  int x = bp(a, b / 2, m);
  x = x * x % m;
  x *= max(1ll, (b % 2) * a);
  return x % m;
}
void solve() {
  int n;
  cin >> n;
  int M = 1e9 + 7;
  int ans = bp(10, n, M);
  vi fact(n + 1);
  fact[0] = 1;
  rep(i, 1, n + 1) fact[i] = fact[i - 1] * i % M;
  rep(i, 1, n) {
    ans -= bp(8, n - i, M) * fact[n] % M * bp(fact[i], M - 2, M) % M *
           bp(fact[n - i], M - 2, M) % M * 2;
    ans = (ans % M + M) % M;
  }
  ans -= bp(8, n, M);
  ans -= 2;
  put((ans + M * 10) % M);
}

signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout.precision(30);
  //    freopen("input.txt", "r", stdin);
  int q = 1;
  //    cin >> q;

  while (q--)
    solve();
}