Problem p02596 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < (n); i++)
#define REP1(i, n) for (int i = 1; i <= (n); i++)
#define REPD(i, a, b) for (int i = (a); i <= (b); i++)
#define ALL(v) (v).begin(), (v).end()
using namespace std;
typedef long long ll;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef set<int> si;
typedef vector<si> vsi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef pair<int, int> pi;
typedef queue<int> qi;
typedef queue<pi> qpi;
typedef pair<ll, ll> pll;
typedef queue<pll> qpll;
typedef vector<pi> vpi;
typedef vector<pll> vpll;
const int mod = 1000000007;
const int INF = 1001001001;
// 小数点　<< fixed << setprecision(0) <<
// sort降順　sort(ALL(),greater<int>());
// 円周率　M_PI
// 文字判定　isupper islower
// 文字変換　
// 順列　do {} while(next_permutation(ALL(X)));
// 最大値　LLONG_MAX
// a内でx以上　auto iter = lower_bound(ALL(a), x);
// a内でxより大きい　auto iter = upper_bound(ALL(a), x);
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, 1, -1, 1, -1};
struct edge {
  int from; // 出発点
  int to;   // 到達点
  int cost; // 移動コスト
};
typedef struct edge se;
typedef vector<edge> ve;
unsigned Euclidean_gcd(unsigned a, unsigned b) {
  if (a < b)
    return Euclidean_gcd(b, a);
  unsigned r;
  while ((r = a % b)) {
    a = b;
    b = r;
  }
  return b;
}

int digit_sum(int n) {
  int sum = n % 10;
  while (n != 0) {
    n /= 10;
    sum += n % 10;
  }
  return sum;
}

vpll PrimeFactorization(ll n) {
  vpll res;
  for (ll i = 2; i * i <= n; i++) {
    if (n % i != 0)
      continue;
    ll ex = 0;
    while (n % i == 0) {
      ex++;
      n /= i;
    }
    res.push_back(pll(i, ex));
  }
  if (n != 1)
    res.push_back(pll(n, 1));
  return res;
}

int main() {
  int k;
  cin >> k;
  if (k % 2 == 0) {
    cout << "-1" << endl;
    return 0;
  }
  int w = 7 % k;
  int x = w;
  int cnt = 1;
  while (w != 0) {
    w = (w * 10 + x) % k;
    cnt++;
  }
  cout << cnt << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < (n); i++)
#define REP1(i, n) for (int i = 1; i <= (n); i++)
#define REPD(i, a, b) for (int i = (a); i <= (b); i++)
#define ALL(v) (v).begin(), (v).end()
using namespace std;
typedef long long ll;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef set<int> si;
typedef vector<si> vsi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef pair<int, int> pi;
typedef queue<int> qi;
typedef queue<pi> qpi;
typedef pair<ll, ll> pll;
typedef queue<pll> qpll;
typedef vector<pi> vpi;
typedef vector<pll> vpll;
const int mod = 1000000007;
const int INF = 1001001001;
// 小数点　<< fixed << setprecision(0) <<
// sort降順　sort(ALL(),greater<int>());
// 円周率　M_PI
// 文字判定　isupper islower
// 文字変換　
// 順列　do {} while(next_permutation(ALL(X)));
// 最大値　LLONG_MAX
// a内でx以上　auto iter = lower_bound(ALL(a), x);
// a内でxより大きい　auto iter = upper_bound(ALL(a), x);
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, 1, -1, 1, -1};
struct edge {
  int from; // 出発点
  int to;   // 到達点
  int cost; // 移動コスト
};
typedef struct edge se;
typedef vector<edge> ve;
unsigned Euclidean_gcd(unsigned a, unsigned b) {
  if (a < b)
    return Euclidean_gcd(b, a);
  unsigned r;
  while ((r = a % b)) {
    a = b;
    b = r;
  }
  return b;
}

int digit_sum(int n) {
  int sum = n % 10;
  while (n != 0) {
    n /= 10;
    sum += n % 10;
  }
  return sum;
}

vpll PrimeFactorization(ll n) {
  vpll res;
  for (ll i = 2; i * i <= n; i++) {
    if (n % i != 0)
      continue;
    ll ex = 0;
    while (n % i == 0) {
      ex++;
      n /= i;
    }
    res.push_back(pll(i, ex));
  }
  if (n != 1)
    res.push_back(pll(n, 1));
  return res;
}

int main() {
  int k;
  cin >> k;
  if (k % 2 == 0) {
    cout << "-1" << endl;
    return 0;
  }
  int w = 7 % k;
  int x = w;
  int cnt = 1;
  while (w != 0) {
    w = (w * 10 + x) % k;
    cnt++;
    if (cnt > k) {
      cout << "-1" << endl;
      return 0;
    }
  }
  cout << cnt << endl;
  return 0;
}