Problem p02596 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;

#define rep(i, n) for (lint i = 0; i < n; i++)
#define repr(i, n) for (lint i = n - 1; i >= 0; i--)
#define repi(i, ini, n) for (lint i = ini; i < n; i++)
#define repir(i, ini, n) for (lint i = n - 1; i >= ini; i--)
#define repb(i, start, end) for (lint i = start; i <= end; i++)
#define repbr(i, start, end) for (lint i = end; i >= start; i--)

#define bit(n) (1LL << (n))

#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rg(v, ini, end) v.begin() + ini, v.begin() + end

#define ret return 0;
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)

using lint = long long;
using ulint = unsigned long long;
using ld = long double;
struct xy {
  lint x, y;
  xy() : x(0), y(0) {}
  xy(lint _x, lint _y) : x(_x), y(_y) {}
  xy operator+(const xy &p) const { return xy(x + p.x, y + p.y); }
  bool operator<(xy p) const {
    if (y == p.y)
      return x < p.x;
    return y < p.y;
  }
};
struct xyd {
  ld x, y;
  xyd() : x(0), y(0) {}
  xyd(long double _x, long double _y) : x(_x), y(_y) {}
};
using vec = vector<lint>;
using vecd = vector<ld>;
using vecs = vector<string>;
using vecp = vector<xy>;
template <class T> using vect = vector<T>;
class vec2 : public vector<vector<lint>> {
public:
  vec2() {}
  vec2(lint n) : vector(n) {}
  vec2(lint h, lint w) : vector(h, vector<lint>(w)) {}
  vec2(lint h, lint w, lint v) : vector(h, vector<lint>(w, v)) {}
};

template <class T> using priq = priority_queue<T>;
template <class T> using rpriq = priority_queue<T, vector<T>, greater<T>>;
template <class Key, class Val> using hashmap = unordered_map<Key, Val>;
template <class Key> using hashset = unordered_set<Key>;

template <class It> constexpr typename It::value_type rmax(It begin, It end) {
  return *max_element(begin, end);
}

template <class T1, class T2> constexpr auto mmax(T1 arg1, T2 arg2) {
  using T = decltype(arg1 + arg2);
  return max(T(arg1), T(arg2));
}

template <class T, class... Types> constexpr auto mmax(T arg0, Types... args) {
  return mmax(arg0, mmax(args...));
}

template <class It> constexpr typename It::value_type rmin(It begin, It end) {
  return *min_element(begin, end);
}

template <class T1, class T2> constexpr auto mmin(T1 arg1, T2 arg2) {
  using T = decltype(arg1 + arg2);
  return min(T(arg1), T(arg2));
}

template <class T, class... Types> constexpr auto mmin(T arg0, Types... args) {
  return mmin(arg0, mmin(args...));
}

mt19937 mtrand((random_device())());

const double pi = 3.141592653589793238462;
const lint intmax = 9223372036854775807;
const lint inf = 1100100100100100100LL;

constexpr lint div2(lint p, lint q) { return (p + q - 1) / q; }

#if (__cplusplus < 201703L)

lint gcd(lint a, lint b) {
  while (1) {
    if (a < b)
      swap(a, b);
    if (!b)
      break;
    a %= b;
  }
  return a;
}

lint lcm(lint a, lint b) { return a / gcd(a, b) * b; }

#endif

template <class T> struct nval {
  lint n; // counts
  T val;
  nval() : n(0){};
  nval(lint _n, T _val) : n(_n), val(_val){};
};

template <class It, class It2> auto spacel(It i, It2 end) {
  if (i + 1 == end) {
    return '\n';
  } else {
    return ' ';
  }
}

ostream &setp(ostream &ost) {
  cout << setprecision(60) << fixed;
  return ost;
}

const ulint mod = 1000000007;
// const ulint mod = 998244353;
const ld eps = 0.0000001;

int main() {
  lint k;
  cin >> k;
  if (k % 2 == 0) {
    cout << -1 << endl;
    ret;
  }

  lint n = 7, d = 7, i = 1;
  while (1) {
    if (n % k == 0) {
      cout << i << endl;
      break;
    }
    d *= 10;
    n += d;
    d %= k;
    n %= k;
    i++;
  }

  return 0;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;

#define rep(i, n) for (lint i = 0; i < n; i++)
#define repr(i, n) for (lint i = n - 1; i >= 0; i--)
#define repi(i, ini, n) for (lint i = ini; i < n; i++)
#define repir(i, ini, n) for (lint i = n - 1; i >= ini; i--)
#define repb(i, start, end) for (lint i = start; i <= end; i++)
#define repbr(i, start, end) for (lint i = end; i >= start; i--)

#define bit(n) (1LL << (n))

#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rg(v, ini, end) v.begin() + ini, v.begin() + end

#define ret return 0;
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)

using lint = long long;
using ulint = unsigned long long;
using ld = long double;
struct xy {
  lint x, y;
  xy() : x(0), y(0) {}
  xy(lint _x, lint _y) : x(_x), y(_y) {}
  xy operator+(const xy &p) const { return xy(x + p.x, y + p.y); }
  bool operator<(xy p) const {
    if (y == p.y)
      return x < p.x;
    return y < p.y;
  }
};
struct xyd {
  ld x, y;
  xyd() : x(0), y(0) {}
  xyd(long double _x, long double _y) : x(_x), y(_y) {}
};
using vec = vector<lint>;
using vecd = vector<ld>;
using vecs = vector<string>;
using vecp = vector<xy>;
template <class T> using vect = vector<T>;
class vec2 : public vector<vector<lint>> {
public:
  vec2() {}
  vec2(lint n) : vector(n) {}
  vec2(lint h, lint w) : vector(h, vector<lint>(w)) {}
  vec2(lint h, lint w, lint v) : vector(h, vector<lint>(w, v)) {}
};

template <class T> using priq = priority_queue<T>;
template <class T> using rpriq = priority_queue<T, vector<T>, greater<T>>;
template <class Key, class Val> using hashmap = unordered_map<Key, Val>;
template <class Key> using hashset = unordered_set<Key>;

template <class It> constexpr typename It::value_type rmax(It begin, It end) {
  return *max_element(begin, end);
}

template <class T1, class T2> constexpr auto mmax(T1 arg1, T2 arg2) {
  using T = decltype(arg1 + arg2);
  return max(T(arg1), T(arg2));
}

template <class T, class... Types> constexpr auto mmax(T arg0, Types... args) {
  return mmax(arg0, mmax(args...));
}

template <class It> constexpr typename It::value_type rmin(It begin, It end) {
  return *min_element(begin, end);
}

template <class T1, class T2> constexpr auto mmin(T1 arg1, T2 arg2) {
  using T = decltype(arg1 + arg2);
  return min(T(arg1), T(arg2));
}

template <class T, class... Types> constexpr auto mmin(T arg0, Types... args) {
  return mmin(arg0, mmin(args...));
}

mt19937 mtrand((random_device())());

const double pi = 3.141592653589793238462;
const lint intmax = 9223372036854775807;
const lint inf = 1100100100100100100LL;

constexpr lint div2(lint p, lint q) { return (p + q - 1) / q; }

#if (__cplusplus < 201703L)

lint gcd(lint a, lint b) {
  while (1) {
    if (a < b)
      swap(a, b);
    if (!b)
      break;
    a %= b;
  }
  return a;
}

lint lcm(lint a, lint b) { return a / gcd(a, b) * b; }

#endif

template <class T> struct nval {
  lint n; // counts
  T val;
  nval() : n(0){};
  nval(lint _n, T _val) : n(_n), val(_val){};
};

template <class It, class It2> auto spacel(It i, It2 end) {
  if (i + 1 == end) {
    return '\n';
  } else {
    return ' ';
  }
}

ostream &setp(ostream &ost) {
  cout << setprecision(60) << fixed;
  return ost;
}

const ulint mod = 1000000007;
// const ulint mod = 998244353;
const ld eps = 0.0000001;

int main() {
  lint k;
  cin >> k;
  if (k % 2 == 0 || k % 5 == 0) {
    cout << -1 << endl;
    ret;
  }

  lint n = 7, d = 7, i = 1;
  while (1) {
    if (n % k == 0) {
      cout << i << endl;
      break;
    }
    d *= 10;
    n += d;
    d %= k;
    n %= k;
    i++;
  }

  return 0;
}