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

#include <algorithm>
#include <bit>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdint>
#include <cstring>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <time.h>
#include <tuple>
#include <vector>
using namespace std;
const double PI = 3.14159265358979323846;
const long long int MOD = 1000000000 + 7;
using ll = long long;

struct UnionFind {
  vector<int> parent;

  UnionFind(int N) : parent(N) {
    for (int i = 0; i < N; i++) {
      parent[i] = -1;
    }
  }

  int root(int i) {
    if (parent[i] < 0) {
      return i;
    }
    return (parent[i] = root(parent[i]));
  }

  bool unite(int from, int to) {
    int rx = root(from);
    int ry = root(to);
    if (rx != ry) {
      parent[ry] += parent[rx];
      parent[rx] = ry;

      return true;
    } else {
      return false;
    }
  }

  bool same(int x, int y) { return root(x) == root(y); }

  int treeSize(int x) { return -parent[root(x)]; }
};

long long int modpow(long long int base, long long int pow, long long int mod) {
  if (pow == 1) {
    return base;
  } else if (pow == 0) {
    return 1;
  }

  if (pow % 2 == 0) {
    auto temp = modpow(base, pow / 2, mod);
    return (temp * temp) % mod;
  } else {
    return (base * modpow(base, pow - 1, mod)) % mod;
  }
}

long long int moddiv(long long int X, long long int Y, long long int mod) {
  auto fermatDiv = modpow(Y, mod - 2, mod);

  return (X * fermatDiv) % mod;
}

long long modCombination(long long left, long long right, long long int mod) {
  long long answer = 1;
  if (left > right) {
    for (long long i = 0; i < right; i++) {
      answer = (answer * (left - i)) % mod;
      answer = moddiv(answer, (i + 1), mod);
    }
  }
  return answer;
}

bool IsPrime(long long N) {
  if (N == 1) {
    return false;
  }
  for (long long i = 2; i * i <= N; i++) {
    if (N % i == 0) {
      return false;
    }
  }

  return true;
}

vector<pair<long long, long long>> prime_factorize(long long N) {
  vector<pair<long long, long long>> res;
  for (long long a = 2; a * a <= N; ++a) {
    if (N % a != 0)
      continue;
    long long ex = 0; // 指数

    // 割れる限り割り続ける
    while (N % a == 0) {
      ++ex;
      N /= a;
    }

    // その結果を push
    res.push_back({a, ex});
  }

  // 最後に残った数について
  if (N != 1)
    res.push_back({N, 1});
  return res;
}

vector<long long> enum_divisors(long long N) {
  vector<long long> res;
  for (long long i = 1; i * i <= N; ++i) {
    if (N % i == 0) {
      res.push_back(i);
      // 重複しないならば i の相方である N/i も push
      if (N / i != i)
        res.push_back(N / i);
    }
  }
  // 小さい順に並び替える
  sort(res.begin(), res.end());
  return res;
}

long long gcd(long long a, long long b) {
  if (b > a) {
    long long temp = b;
    b = a;
    a = temp;
  }
  // cout << "a:" << a << "b:" << b << endl;
  long long c = a % b;
  if (c == 0) {
    return b;
  } else {
    return gcd(b, c);
  }
}

int main() {
  ll K;
  cin >> K;
  /*vector<int> digits(100000000);
  int currentDigitsSize = 0;
  ll dummyK = K;
  while (dummyK != 0) {
      digits[currentDigitsSize] = dummyK % 10;
      dummyK = (dummyK - dummyK % 10) / 10;
      currentDigitsSize++;
  }

  int currentBase = 0;
  int first = digits[0];

  bool isOK = false;
  while (true) {
      if (digits[currentBase] == 7) {
          if (currentBase == currentDigitsSize - 1) {
              isOK = true;
              break;
          }
          currentBase++;
          continue;
      }

      int mul = 1;
      for (mul = 1; mul <= 10; mul++) {
          if (mul == 10) {
              break;
          }
          if ((digits[currentBase] + ((mul * first) % 10)) % 10 == 7) {
              break;
          }
      }

      if (mul == 10) {
          break;
      }

      int offset = 0;
      int over = 0;
      int plusK = K * mul;

      while (plusK != 0 || over != 0) {
          if (currentBase + offset < currentDigitsSize) {
              digits[currentBase + offset] += (plusK % 10) + over;
              plusK = (plusK - plusK % 10) / 10;

              over = (digits[currentBase + offset] - (digits[currentBase +
  offset] % 10)) / 10; digits[currentBase + offset] -= over * 10;
          }
          else {
              digits[currentDigitsSize] = plusK % 10 + over;
              currentDigitsSize++;

              plusK = (plusK - plusK % 10) / 10;

              over = (digits[currentBase + offset] - (digits[currentBase +
  offset] % 10)) / 10; digits[currentBase + offset] -= over * 10;
          }

          offset++;
      }

      currentBase++;
  }

  if (isOK) {
      cout << currentDigitsSize << endl;
  }
  else {
      cout << -1 << endl;
  }*/

  int count = 0;
  int digitsCount = 0;
  ll total = K;
  while (count <= 9) {
    // cout << total << endl;
    if (total % 10 == 7) {
      total /= 10;
      count = 0;
      digitsCount++;
      if (total == 0) {
        break;
      }
      continue;
    } else {
      count++;
    }
    total += K;
  }

  if (count == 10) {
    cout << -1 << endl;
  } else {
    cout << digitsCount << endl;
  }
  return 0;
}


Error: TLE

Fixed submission:

#include <algorithm>
#include <bit>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdint>
#include <cstring>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <time.h>
#include <tuple>
#include <vector>
using namespace std;
const double PI = 3.14159265358979323846;
const long long int MOD = 1000000000 + 7;
using ll = long long;

struct UnionFind {
  vector<int> parent;

  UnionFind(int N) : parent(N) {
    for (int i = 0; i < N; i++) {
      parent[i] = -1;
    }
  }

  int root(int i) {
    if (parent[i] < 0) {
      return i;
    }
    return (parent[i] = root(parent[i]));
  }

  bool unite(int from, int to) {
    int rx = root(from);
    int ry = root(to);
    if (rx != ry) {
      parent[ry] += parent[rx];
      parent[rx] = ry;

      return true;
    } else {
      return false;
    }
  }

  bool same(int x, int y) { return root(x) == root(y); }

  int treeSize(int x) { return -parent[root(x)]; }
};

long long int modpow(long long int base, long long int pow, long long int mod) {
  if (pow == 1) {
    return base;
  } else if (pow == 0) {
    return 1;
  }

  if (pow % 2 == 0) {
    auto temp = modpow(base, pow / 2, mod);
    return (temp * temp) % mod;
  } else {
    return (base * modpow(base, pow - 1, mod)) % mod;
  }
}

long long int moddiv(long long int X, long long int Y, long long int mod) {
  auto fermatDiv = modpow(Y, mod - 2, mod);

  return (X * fermatDiv) % mod;
}

long long modCombination(long long left, long long right, long long int mod) {
  long long answer = 1;
  if (left > right) {
    for (long long i = 0; i < right; i++) {
      answer = (answer * (left - i)) % mod;
      answer = moddiv(answer, (i + 1), mod);
    }
  }
  return answer;
}

bool IsPrime(long long N) {
  if (N == 1) {
    return false;
  }
  for (long long i = 2; i * i <= N; i++) {
    if (N % i == 0) {
      return false;
    }
  }

  return true;
}

vector<pair<long long, long long>> prime_factorize(long long N) {
  vector<pair<long long, long long>> res;
  for (long long a = 2; a * a <= N; ++a) {
    if (N % a != 0)
      continue;
    long long ex = 0; // 指数

    // 割れる限り割り続ける
    while (N % a == 0) {
      ++ex;
      N /= a;
    }

    // その結果を push
    res.push_back({a, ex});
  }

  // 最後に残った数について
  if (N != 1)
    res.push_back({N, 1});
  return res;
}

vector<long long> enum_divisors(long long N) {
  vector<long long> res;
  for (long long i = 1; i * i <= N; ++i) {
    if (N % i == 0) {
      res.push_back(i);
      // 重複しないならば i の相方である N/i も push
      if (N / i != i)
        res.push_back(N / i);
    }
  }
  // 小さい順に並び替える
  sort(res.begin(), res.end());
  return res;
}

long long gcd(long long a, long long b) {
  if (b > a) {
    long long temp = b;
    b = a;
    a = temp;
  }
  // cout << "a:" << a << "b:" << b << endl;
  long long c = a % b;
  if (c == 0) {
    return b;
  } else {
    return gcd(b, c);
  }
}

int main() {
  ll K;
  cin >> K;
  vector<int> digits(100000000);
  int currentDigitsSize = 0;
  ll dummyK = K;
  while (dummyK != 0) {
    digits[currentDigitsSize] = dummyK % 10;
    dummyK = (dummyK - dummyK % 10) / 10;
    currentDigitsSize++;
  }

  int currentBase = 0;
  int first = digits[0];

  bool isOK = false;
  while (true) {
    if (digits[currentBase] == 7) {
      if (currentBase == currentDigitsSize - 1) {
        isOK = true;
        break;
      }
      currentBase++;
      continue;
    }

    int mul = 1;
    for (mul = 1; mul <= 10; mul++) {
      if (mul == 10) {
        break;
      }
      if ((digits[currentBase] + ((mul * first) % 10)) % 10 == 7) {
        break;
      }
    }

    if (mul == 10) {
      break;
    }

    int offset = 0;
    int over = 0;
    int plusK = K * mul;

    while (plusK != 0 || over != 0) {
      if (currentBase + offset < currentDigitsSize) {
        digits[currentBase + offset] += (plusK % 10) + over;
        plusK = (plusK - plusK % 10) / 10;

        over = (digits[currentBase + offset] -
                (digits[currentBase + offset] % 10)) /
               10;
        digits[currentBase + offset] -= over * 10;
      } else {
        digits[currentDigitsSize] = plusK % 10 + over;
        currentDigitsSize++;

        plusK = (plusK - plusK % 10) / 10;

        over = (digits[currentBase + offset] -
                (digits[currentBase + offset] % 10)) /
               10;
        digits[currentBase + offset] -= over * 10;
      }

      offset++;
    }

    /*for (int i = digits.size() - 1; i >= 0; i--) {
        cout << digits[i];
    }
    cout << endl;*/
    currentBase++;
  }

  if (isOK) {
    cout << currentDigitsSize << endl;
  } else {
    cout << -1 << endl;
  }
  return 0;
}