Problem p02596 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
// #include <ext/pb_ds/assoc_container.hpp>
// using namespace __gnu_pbds;
// typedef tree <int,null_type,less <int>, rb_tree_tag,
// tree_order_statistics_node_update> indexed_set;
//  #include <ext/rope>
//  using namespace __gnu_cxx;
typedef long long int ll;
typedef long double ld;
#define FAST                                                                   \\
  ios::sync_with_stdio(0);                                                     \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define rep(g, i, n) for (ll g = i; g < n; g++)
#define rev(g, n, i) for (ll g = n - 1; g >= i; g--)
#define all(v) v.begin(), v.end()
#define pb push_back
#define mxe(v) *max_element(v.begin(), v.end())
#define mne(v) *min_element(v.begin(), v.end())
#define ve vector
#define lb lower_bound
#define ub upper_bound
#define bb break
#define cc continue
#define rem 1000000007
#define PI 3.141592653589793238462643383279502
ll power(ll x, ll y, ll p) {
  ll res = 1; // Initialize result
  x = x % p;  // Update x if it is more than or
  while (y > 0) {
    if (y & 1)
      res = (res * x) % p;
    y = y >> 1; // y = y/2
    x = (x * x) % p;
  }
  return res;
}
ll modInverse(ll n, ll p) { return power(n, p - 2, p); }
struct point {
  ll x, y;
};
int main() {
  FAST
      // freopen("input1.txt", "r", stdin);
      // freopen("output.txt", "w", stdout);
      /*ll tests;
      cin>>tests;
      rep (gg,0,tests)
      {}*/
      ll k;
  cin >> k;
  ll ans = 0;
  rep(i, 1, 1000000) {
    ll val = 7 * power(10, i - 1, k);
    ans += val;
    ans %= k;
    if (ans == 0) {
      cout << i << "\\n";
      return 0;
    }
  }
  cout << "-1\\n";
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
// #include <ext/pb_ds/assoc_container.hpp>
// using namespace __gnu_pbds;
// typedef tree <int,null_type,less <int>, rb_tree_tag,
// tree_order_statistics_node_update> indexed_set;
//  #include <ext/rope>
//  using namespace __gnu_cxx;
typedef long long int ll;
typedef long double ld;
#define FAST                                                                   \\
  ios::sync_with_stdio(0);                                                     \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define rep(g, i, n) for (ll g = i; g < n; g++)
#define rev(g, n, i) for (ll g = n - 1; g >= i; g--)
#define all(v) v.begin(), v.end()
#define pb push_back
#define mxe(v) *max_element(v.begin(), v.end())
#define mne(v) *min_element(v.begin(), v.end())
#define ve vector
#define lb lower_bound
#define ub upper_bound
#define bb break
#define cc continue
#define rem 1000000007
#define PI 3.141592653589793238462643383279502
ll power(ll x, ll y, ll p) {
  ll res = 1; // Initialize result
  x = x % p;  // Update x if it is more than or
  while (y > 0) {
    if (y & 1)
      res = (res * x) % p;
    y = y >> 1; // y = y/2
    x = (x * x) % p;
  }
  return res;
}
ll modInverse(ll n, ll p) { return power(n, p - 2, p); }
struct point {
  ll x, y;
};
int main() {
  FAST
      // freopen("input1.txt", "r", stdin);
      // freopen("output.txt", "w", stdout);
      /*ll tests;
      cin>>tests;
      rep (gg,0,tests)
      {}*/
      ll k;
  cin >> k;
  ll ans = 0;
  rep(i, 1, 10000000) {
    ll val = 7 * power(10, i - 1, k);
    ans += val;
    ans %= k;
    if (ans == 0) {
      cout << i << "\\n";
      return 0;
    }
  }
  cout << "-1\\n";
}