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

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ull unsigned long long
#define pb push_back
#define pf push_front
#define pof pop_front
#define pob pop_back
#define mp make_pair
#define pll pair<ll, ll>
#define pii pair<int, int>
#define all(s) s.begin(), s.end()
#define vll vector<ll>
#define vi vector<int>
#define vpii vector<pii>
#define vpll vector<pll>
#define vd vector<double>
#define vull vector<ull>
#define vc vector<char>
#define vs vector<string>
#define fi first
#define se second
#define sz(x) x.size()
#define cinarr(n, a)                                                           \\
  for (int i = 0; i < n; i++)                                                  \\
    cin >> a[i];
#define coutarr(n, a)                                                          \\
  for (int i = 0; i < n; i++)                                                  \\
    cout << a[i] << (i + 1 == n ? '\\n' : ' ');
#define fori(i, a, b, x) for (int i = a; i <= b; i += x)
#define ford(i, a, b, x) for (int i = a; i >= b; i -= x)
#define tc                                                                     \\
  int tt;                                                                      \\
  cin >> tt;                                                                   \\
  for (int cs = 1; cs <= tt; cs++)
#define IOS                                                                    \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(NULL);
#define ld long double
#define reset(x, y) memset(x, y, sizeof x);
#define sqr(x) 1LL * (x) * (x)
#define cube(x) 1LL * (x) * (x) * (x)
#define ub(v, a) upper_bound(all(v), a)
#define lb(v, a) lower_bound(all(v), a)
#define EPS 1e-10
#define INF 200000
#define mod 1000000007
#define minof(a) min_element(all(a))
#define maxof(a) max_element(all(a))
#define debug(val) cout << "The value of " << #val << " is = " << val << endl;
#define testing cout << "--------------------------\\n";

int main() {
  IOS int n;
  cin >> n;
  if (n % 2 == 0) {
    cout << "-1\\n";
    return 0;
  }
  int cur = 1, nw = 7 % n;
  while (nw) {
    nw = (nw * 10 + 7) % n;
    cur++;
    if (cur > 1e7) {
      cout << "-1\\n";
      return 0;
    }
  }
  cout << cur << endl;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ull unsigned long long
#define pb push_back
#define pf push_front
#define pof pop_front
#define pob pop_back
#define mp make_pair
#define pll pair<ll, ll>
#define pii pair<int, int>
#define all(s) s.begin(), s.end()
#define vll vector<ll>
#define vi vector<int>
#define vpii vector<pii>
#define vpll vector<pll>
#define vd vector<double>
#define vull vector<ull>
#define vc vector<char>
#define vs vector<string>
#define fi first
#define se second
#define sz(x) x.size()
#define cinarr(n, a)                                                           \\
  for (int i = 0; i < n; i++)                                                  \\
    cin >> a[i];
#define coutarr(n, a)                                                          \\
  for (int i = 0; i < n; i++)                                                  \\
    cout << a[i] << (i + 1 == n ? '\\n' : ' ');
#define fori(i, a, b, x) for (int i = a; i <= b; i += x)
#define ford(i, a, b, x) for (int i = a; i >= b; i -= x)
#define tc                                                                     \\
  int tt;                                                                      \\
  cin >> tt;                                                                   \\
  for (int cs = 1; cs <= tt; cs++)
#define IOS                                                                    \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(NULL);
#define ld long double
#define reset(x, y) memset(x, y, sizeof x);
#define sqr(x) 1LL * (x) * (x)
#define cube(x) 1LL * (x) * (x) * (x)
#define ub(v, a) upper_bound(all(v), a)
#define lb(v, a) lower_bound(all(v), a)
#define EPS 1e-10
#define INF 200000
#define mod 1000000007
#define minof(a) min_element(all(a))
#define maxof(a) max_element(all(a))
#define debug(val) cout << "The value of " << #val << " is = " << val << endl;
#define testing cout << "--------------------------\\n";

int main() {
  IOS int n;
  cin >> n;
  if (n % 2 == 0) {
    cout << "-1\\n";
    return 0;
  }
  int cur = 1, nw = 7 % n;
  while (nw) {
    nw = (nw * 10 + 7) % n;
    cur++;
  }
  cout << cur << endl;
}