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

// g++ t.cpp -o t && t < p.txt
// d>p.txt&&t<p.txt&&t2<p.txt

#include <algorithm> // みんな大好きソートと二分探索
#include <ctime>
#include <functional> // 関数を変数に入れる子
#include <iostream>   // プログラムの耳と口
#include <map>        // setの妹 これまた優秀
#include <queue>      // きゅーちゃん、だいすき
#include <random>     // 乱択さん
#include <set>        // 値の取得・挿入・削除を高速に
#include <string>     // to_string
#include <vector>     // 超有能配列秘書

#define DB cerr << "D" << endl
using namespace std;
using ll = long long;
using ld = long double;
const int INF = 1e9;
const ll LINF = 1e18;
const double dINF = 1e18;
const ld ldINF = 1e18;
const double EPS = 1e-6;
template <typename T, typename U, typename O> void caut(T a, U b, O c) {
  cout << "(" << a << "," << b << "," << c << ") ";
}
template <typename T, typename U> void caut(T a, U b) {
  cout << "(" << a << "," << b << ") ";
}
template <typename T> void caut(T a) { cout << "(" << a << ") "; };
using P = pair<ll, ll>;
const ll M = 1e9 + 7;
ll mod_pow(ll x, ll a) {
  ll an = 1;
  while (a > 0) {
    if (a & 1)
      an = an * x % M;
    x = x * x % M;
    a >>= 1;
  }
  return an;
}
void add(ll &x, ll y) {
  x += y;
  x %= M;
};
void mul(ll &x, ll y) {
  x *= y;
  x %= M;
};
template <typename T, typename U> void chmax(T &x, U y) {
  if (x < y)
    x = y;
};
template <typename T, typename U> void chmin(T &x, U y) {
  if (x > y)
    x = y;
}
bool vaild(int x, int y, int hh, int ww) {
  return 0 <= x && x < hh && 0 <= y && y < ww;
}
int keta(ll a) {
  int res = 0;
  while (a > 0)
    res += a % 10, a /= 10;
  return res;
}

int main() {
  ll k;
  cin >> k;
  ll x = 7 % k, t = 1;
  bool u[k] = {};
  u[x] = true;
  while (x != 0) {
    x = x * 10 + 7;
    x %= k;
    t++;
    if (u[x]) {
      cout << -1 << endl;
      return 0;
    }
    u[x] = true;
  }
  cout << t << endl;
}
// ・配列の大きさok？　・priority_queueはgreater？　・debug消した？
// ・落ち着いて。提出まで4分待ってね……WJ……1/10……2/10……

// Thank you for making problems and running the contest


Error: TLE

Fixed submission:

// g++ t.cpp -o t && t < p.txt
// d>p.txt&&t<p.txt&&t2<p.txt

#include <algorithm> // みんな大好きソートと二分探索
#include <ctime>
#include <functional> // 関数を変数に入れる子
#include <iostream>   // プログラムの耳と口
#include <map>        // setの妹 これまた優秀
#include <queue>      // きゅーちゃん、だいすき
#include <random>     // 乱択さん
#include <set>        // 値の取得・挿入・削除を高速に
#include <string>     // to_string
#include <vector>     // 超有能配列秘書

#define DB cerr << "D" << endl
using namespace std;
using ll = long long;
using ld = long double;
const int INF = 1e9;
const ll LINF = 1e18;
const double dINF = 1e18;
const ld ldINF = 1e18;
const double EPS = 1e-6;
template <typename T, typename U, typename O> void caut(T a, U b, O c) {
  cout << "(" << a << "," << b << "," << c << ") ";
}
template <typename T, typename U> void caut(T a, U b) {
  cout << "(" << a << "," << b << ") ";
}
template <typename T> void caut(T a) { cout << "(" << a << ") "; };
using P = pair<ll, ll>;
const ll M = 1e9 + 7;
ll mod_pow(ll x, ll a) {
  ll an = 1;
  while (a > 0) {
    if (a & 1)
      an = an * x % M;
    x = x * x % M;
    a >>= 1;
  }
  return an;
}
void add(ll &x, ll y) {
  x += y;
  x %= M;
};
void mul(ll &x, ll y) {
  x *= y;
  x %= M;
};
template <typename T, typename U> void chmax(T &x, U y) {
  if (x < y)
    x = y;
};
template <typename T, typename U> void chmin(T &x, U y) {
  if (x > y)
    x = y;
}
bool vaild(int x, int y, int hh, int ww) {
  return 0 <= x && x < hh && 0 <= y && y < ww;
}
int keta(ll a) {
  int res = 0;
  while (a > 0)
    res += a % 10, a /= 10;
  return res;
}

int main() {
  ll k;
  cin >> k;
  if (k % 2 == 0) {
    cout << -1 << endl;
    return 0;
  }
  ll x = 7 % k, t = 1;
  while (x != 0) {
    x = x * 10 + 7;
    x %= k;
    t++;
  }
  cout << t << endl;
}
// ・配列の大きさok？　・priority_queueはgreater？　・debug消した？
// ・落ち着いて。提出まで4分待ってね……WJ……1/10……2/10……

// Thank you for making problems and running the contest