Problem p03178 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;

#define TemplateVersion "3.7.1"
// Useful Marcos
//====================START=====================
// Compile use C++11 and above
#ifdef LOCAL
#define debug(args...)                                                         \
  do {                                                                         \
    string _s = #args;                                                         \
    replace(_s.begin(), _s.end(), ',', ' ');                                   \
    stringstream _ss(_s);                                                      \
    istream_iterator<string> _it(_ss);                                         \
    err(_it, args);                                                            \
  } while (0)
void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << endl;
  err(++it, args...);
}
#define MSG cout << "Finished" << endl
#else
#define debug(args...)
#define MSG
#endif
#if __cplusplus >= 201703L
template <typename... Args> void readln(Args &...args) { ((cin >> args), ...); }
template <typename... Args> void writeln(Args... args) {
  ((cout << args << " "), ...);
  cout << endl;
}
#elif __cplusplus >= 201103L
void readln() {}
template <typename T, typename... Args> void readln(T &a, Args &...args) {
  cin >> a;
  readln(args...);
}
void writeln() { cout << endl; }
template <typename T, typename... Args> void writeln(T a, Args... args) {
  cout << a << " ";
  writeln(args...);
}
#endif
#if __cplusplus >= 201103L
#define FOR(_i, _begin, _end) for (auto _i = _begin; _i < _end; _i++)
#define FORR(_i, _begin, _end) for (auto _i = _begin; _i > _end; _i--)
#else
#define FOR(_i, _begin, _end) for (int _i = (int)_begin; _i < (int)_end; _i++)
#define FORR(_i, _begin, _end) for (int _i = (int)_begin; _i > (int)_end; _i--)
#define nullptr NULL
#endif
#if __cplusplus >= 201103L
#define VIS(_kind, _name, _size)                                               \
  vector<_kind> _name(_size);                                                  \
  for (auto &i : _name)                                                        \
    cin >> i;
#else
#define VIS(_kind, _name, _size)                                               \
  vector<_kind> _name;                                                         \
  _name.resize(_size);                                                         \
  for (int i = 0; i < _size; i++)                                              \
    cin >> _name[i];
#endif
// alias
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define clr(x) memset((x), 0, sizeof(x))
#define infty(x) memset((x), 0x3f, sizeof(x))
#define tcase()                                                                \
  int T;                                                                       \
  cin >> T;                                                                    \
  FOR(kase, 1, T + 1)

// Swap max/min
template <typename T> bool smax(T &a, const T &b) {
  if (a > b)
    return false;
  a = b;
  return true;
}
template <typename T> bool smin(T &a, const T &b) {
  if (a < b)
    return false;
  a = b;
  return true;
}
// ceil divide
template <typename T> T cd(T a, T b) { return (a + b - 1) / b; }
// min exchange
template <typename T> bool se(T &a, T &b) {
  if (a < b)
    return false;
  swap(a, b);
  return true;
}
// A better MAX choice
const int INF = 0x3f3f3f3f;
const long long INFLL = 0x3f3f3f3f3f3f3f3fLL;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef set<int> si;
typedef vector<string> cb;
//====================END=====================

// Constants here
const int MAXK = 10010;
const int MAXD = 110;
const int MOD = 1e9 + 7;

int num[MAXK];
ll memo[MAXK][MAXD];
int D;

ll dfs(int pos, int rem, bool limit) {
  if (pos == -1) {
    return rem == 0;
  }

  if (!limit && memo[pos][rem] != -1) {
    return memo[pos][rem];
  }

  ll ans = 0;

  int maxx = limit ? num[pos] : 9;

  for (int i = 0; i <= maxx; i++) {
    ans = (ans + dfs(pos - 1, (rem + i) % D, limit && i == num[pos])) % MOD;
  }

  if (!limit) {
    memo[pos][rem] = ans;
  }

  return ans;
}

// Pre-Build Function
inline void build() { memset(memo, -1, sizeof memo); }

// Actual Solver
inline void solve() {
  string K;
  readln(K, D);
  D %= 100;

  int len = K.size();

  for (int i = len - 1; i >= 0; i--) {
    num[i] = K[len - i - 1] - '0';
  }

  writeln((dfs(len - 1, 0, true) + MOD - 1) % MOD);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);

#ifdef LOCAL
  clock_t _begin = clock();
#endif

  build();
  solve();

#ifdef LOCAL
  cerr << "Time elapsed: " << (double)(clock() - _begin) * 1000 / CLOCKS_PER_SEC
       << "ms." << endl;
#endif

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>

using namespace std;

#define TemplateVersion "3.7.1"
// Useful Marcos
//====================START=====================
// Compile use C++11 and above
#ifdef LOCAL
#define debug(args...)                                                         \
  do {                                                                         \
    string _s = #args;                                                         \
    replace(_s.begin(), _s.end(), ',', ' ');                                   \
    stringstream _ss(_s);                                                      \
    istream_iterator<string> _it(_ss);                                         \
    err(_it, args);                                                            \
  } while (0)
void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << endl;
  err(++it, args...);
}
#define MSG cout << "Finished" << endl
#else
#define debug(args...)
#define MSG
#endif
#if __cplusplus >= 201703L
template <typename... Args> void readln(Args &...args) { ((cin >> args), ...); }
template <typename... Args> void writeln(Args... args) {
  ((cout << args << " "), ...);
  cout << endl;
}
#elif __cplusplus >= 201103L
void readln() {}
template <typename T, typename... Args> void readln(T &a, Args &...args) {
  cin >> a;
  readln(args...);
}
void writeln() { cout << endl; }
template <typename T, typename... Args> void writeln(T a, Args... args) {
  cout << a << " ";
  writeln(args...);
}
#endif
#if __cplusplus >= 201103L
#define FOR(_i, _begin, _end) for (auto _i = _begin; _i < _end; _i++)
#define FORR(_i, _begin, _end) for (auto _i = _begin; _i > _end; _i--)
#else
#define FOR(_i, _begin, _end) for (int _i = (int)_begin; _i < (int)_end; _i++)
#define FORR(_i, _begin, _end) for (int _i = (int)_begin; _i > (int)_end; _i--)
#define nullptr NULL
#endif
#if __cplusplus >= 201103L
#define VIS(_kind, _name, _size)                                               \
  vector<_kind> _name(_size);                                                  \
  for (auto &i : _name)                                                        \
    cin >> i;
#else
#define VIS(_kind, _name, _size)                                               \
  vector<_kind> _name;                                                         \
  _name.resize(_size);                                                         \
  for (int i = 0; i < _size; i++)                                              \
    cin >> _name[i];
#endif
// alias
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define clr(x) memset((x), 0, sizeof(x))
#define infty(x) memset((x), 0x3f, sizeof(x))
#define tcase()                                                                \
  int T;                                                                       \
  cin >> T;                                                                    \
  FOR(kase, 1, T + 1)

// Swap max/min
template <typename T> bool smax(T &a, const T &b) {
  if (a > b)
    return false;
  a = b;
  return true;
}
template <typename T> bool smin(T &a, const T &b) {
  if (a < b)
    return false;
  a = b;
  return true;
}
// ceil divide
template <typename T> T cd(T a, T b) { return (a + b - 1) / b; }
// min exchange
template <typename T> bool se(T &a, T &b) {
  if (a < b)
    return false;
  swap(a, b);
  return true;
}
// A better MAX choice
const int INF = 0x3f3f3f3f;
const long long INFLL = 0x3f3f3f3f3f3f3f3fLL;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef set<int> si;
typedef vector<string> cb;
//====================END=====================

// Constants here
const int MAXK = 10010;
const int MAXD = 110;
const int MOD = 1e9 + 7;

int num[MAXK];
ll memo[MAXK][MAXD];
int D;

ll dfs(int pos, int rem, bool limit) {
  if (pos == -1) {
    return rem == 0;
  }

  if (!limit && memo[pos][rem] != -1) {
    return memo[pos][rem];
  }

  ll ans = 0;

  int maxx = limit ? num[pos] : 9;

  for (int i = 0; i <= maxx; i++) {
    ans = (ans + dfs(pos - 1, (rem + i) % D, limit && i == num[pos])) % MOD;
  }

  if (!limit) {
    memo[pos][rem] = ans;
  }

  return ans;
}

// Pre-Build Function
inline void build() { memset(memo, -1, sizeof memo); }

// Actual Solver
inline void solve() {
  string K;
  readln(K, D);

  int len = K.size();

  for (int i = len - 1; i >= 0; i--) {
    num[i] = K[len - i - 1] - '0';
  }

  writeln((dfs(len - 1, 0, true) + MOD - 1) % MOD);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);

#ifdef LOCAL
  clock_t _begin = clock();
#endif

  build();
  solve();

#ifdef LOCAL
  cerr << "Time elapsed: " << (double)(clock() - _begin) * 1000 / CLOCKS_PER_SEC
       << "ms." << endl;
#endif

  return 0;
}