Problem p03178 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#include <iostream>
#include <numeric>
#define ll long long
#define mod 1000000007
#define mod1 998244353
using namespace std;
// vector<int>adj[200000+1];
int cnt = 0;
vector<int> cand;
bool prime[100006];
void SieveOfEratosthenes(int n) {

  memset(prime, true, sizeof(prime));

  for (int p = 2; p * p <= n; p++) {
    if (prime[p] == true) {
      for (int i = p * p; i <= n; i += p)
        prime[i] = false;
    }
  }
}
int prob = 0;
void dfs(vector<int> adj[], int v, bool visited[], stack<int> &s,
         bool visited2[]) {

  visited[v] = true;
  int i;
  int c = 1;
  bool f = true;
  for (i = 0; i < adj[v].size(); i++) {
    if (!visited[adj[v][i]]) {
      f = false;
      dfs(adj, adj[v][i], visited, s, visited2);
    }
  }
  if (adj[v].size() == 1) {
    s.push(v);
    visited2[v] = true;
  }
}
long long power(long long x, long long y) {
  long long res = 1;
  x = x % mod;
  if (x == 0)
    return 0;
  while (y > 0) {
    if (y & 1)
      res = (res * x) % mod;
    y = y >> 1;
    x = (x * x) % mod;
  }
  return res;
}
long long add(long long x, long long y) {
  x += y;
  while (x >= mod)
    x -= mod;
  while (x < 0)
    x += mod;
  return x;
}

long long mul(long long x, long long y) { return (x * 1ll * y) % mod; }

long long binpow(long long x, long long y) {
  long long z = 1;
  while (y) {
    if (y & 1)
      z = mul(z, x);
    x = mul(x, x);
    y >>= 1;
  }
  return z;
}

long long inv(long long x) { return binpow(x, mod - 2); }

long long divide(long long x, long long y) { return mul(x, inv(y)); }

long long fact[100005];

void precalc() {
  fact[0] = 1;
  for (long long i = 1; i < 100005; i++)
    fact[i] = mul(fact[i - 1], i);
}

long long C(long long n, long long k) {
  if (n == 0)
    return 1;
  return divide(fact[n], mul(fact[k], fact[n - k]));
}
int dfs(bool visited[], vector<int> adj[], int v) {
  int c = 1;
  visited[v] = true;
  for (int i = 0; i < adj[v].size(); i++) {
    if (!visited[adj[v][i]]) {
      c += dfs(visited, adj, adj[v][i]);
    }
  }
  return c;
}
struct comp {
  bool operator()(const pair<int, int> &p1, const pair<int, int> &p2) {
    if (p1.first == p2.first) {
      return p1.second < p2.second;
    } else
      return p1.first > p2.first;
  }
};
long long sub(long long A, long long B) { return (A - B + mod) % mod; }
void toposort(vector<int> &order, int v, int visited[], vector<int> adj[]) {
  visited[v] = 1;
  int i;
  for (i = 0; i < adj[v].size(); i++) {
    if (!visited[adj[v][i]]) {
      toposort(order, adj[v][i], visited, adj);
    }
  }
  order.push_back(v);
}
ll segtree[4 * 200000 + 1];
void build(ll A[], ll tl, ll tr, ll v) {
  if (tl == tr)
    segtree[v] = A[tl];
  else {
    ll tm = (tl + tr) / 2;
    build(A, tl, tm, v * 2);
    build(A, tm + 1, tr, 2 * v + 1);
    segtree[v] = max(segtree[2 * v], segtree[2 * v + 1]);
  }
}
ll maxival(ll v, ll tl, ll tr, ll l, ll r) {
  if (l > r)
    return 0;
  if (l == tl && r == tr)
    return segtree[v];
  ll tm = (tl + tr) / 2;
  return max(maxival(2 * v, tl, tm, l, min(r, tm)),
             maxival(2 * v + 1, tm + 1, tr, max(l, tm + 1), r));
}
void updateval(ll v, ll tl, ll tr, ll pos, ll newval) {
  if (tl == tr)
    segtree[v] = newval;
  else {
    ll tm = (tl + tr) / 2;
    if (pos <= tm)
      updateval(2 * v, tl, tm, pos, newval);
    else
      updateval(2 * v + 1, tm + 1, tr, pos, newval);
    segtree[v] = max(segtree[2 * v], segtree[2 * v + 1]);
  }
}
ll dp[10000 + 2][100 + 1][2];
long long calcdp(string k, ll d, ll pos, ll rem, ll index) {
  ll i;
  if (index == k.size()) {
    if (rem == 0)
      return 1ll;
    return 0ll;
  }
  if (dp[index][rem][pos] != -1)
    return dp[index][rem][pos];
  dp[index][rem][pos] = 0ll;
  if (pos == 0) {
    for (i = 0; i < k[index] - '0'; i++) {
      dp[index][rem][pos] =
          add(dp[index][rem][pos], calcdp(k, d, 1, (rem + i) % d, index + 1));
    }
    dp[index][rem][pos] =
        add(dp[index][rem][pos], calcdp(k, d, 0, (rem + i) % d, index + 1));
  } else {
    for (i = 0; i <= 9; i++)
      dp[index][rem][pos] =
          add(dp[index][rem][pos], calcdp(k, d, 1, (rem + i) % d, index + 1));
  }
  return dp[index][rem][pos];
}
int main() {

  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cout << fixed << setprecision(10);
  cerr << fixed << setprecision(5);
  int t = 1;
  // SieveOfEratosthenes(100005);
  // precalc();
  // freopen("input.txt","r",stdin);
  // freopen("output.txt","w",stdout);
  // cin>>t;
  while (t--) {
    string k;
    long long d;
    cin >> k >> d;
    memset(dp, -1ll, sizeof(dp));
    cout << (calcdp(k, d, 0, 0, 0) + mod - 1) % mod;
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#include <iostream>
#include <numeric>
#define ll long long
#define mod 1000000007
#define mod1 998244353
using namespace std;
// vector<int>adj[200000+1];
int cnt = 0;
vector<int> cand;
bool prime[100006];
void SieveOfEratosthenes(int n) {

  memset(prime, true, sizeof(prime));

  for (int p = 2; p * p <= n; p++) {
    if (prime[p] == true) {
      for (int i = p * p; i <= n; i += p)
        prime[i] = false;
    }
  }
}
int prob = 0;
void dfs(vector<int> adj[], int v, bool visited[], stack<int> &s,
         bool visited2[]) {

  visited[v] = true;
  int i;
  int c = 1;
  bool f = true;
  for (i = 0; i < adj[v].size(); i++) {
    if (!visited[adj[v][i]]) {
      f = false;
      dfs(adj, adj[v][i], visited, s, visited2);
    }
  }
  if (adj[v].size() == 1) {
    s.push(v);
    visited2[v] = true;
  }
}
long long power(long long x, long long y) {
  long long res = 1;
  x = x % mod;
  if (x == 0)
    return 0;
  while (y > 0) {
    if (y & 1)
      res = (res * x) % mod;
    y = y >> 1;
    x = (x * x) % mod;
  }
  return res;
}
long long add(long long x, long long y) {
  x += y;
  while (x >= mod)
    x -= mod;
  while (x < 0)
    x += mod;
  return x;
}

long long mul(long long x, long long y) { return (x * 1ll * y) % mod; }

long long binpow(long long x, long long y) {
  long long z = 1;
  while (y) {
    if (y & 1)
      z = mul(z, x);
    x = mul(x, x);
    y >>= 1;
  }
  return z;
}

long long inv(long long x) { return binpow(x, mod - 2); }

long long divide(long long x, long long y) { return mul(x, inv(y)); }

long long fact[100005];

void precalc() {
  fact[0] = 1;
  for (long long i = 1; i < 100005; i++)
    fact[i] = mul(fact[i - 1], i);
}

long long C(long long n, long long k) {
  if (n == 0)
    return 1;
  return divide(fact[n], mul(fact[k], fact[n - k]));
}
int dfs(bool visited[], vector<int> adj[], int v) {
  int c = 1;
  visited[v] = true;
  for (int i = 0; i < adj[v].size(); i++) {
    if (!visited[adj[v][i]]) {
      c += dfs(visited, adj, adj[v][i]);
    }
  }
  return c;
}
struct comp {
  bool operator()(const pair<int, int> &p1, const pair<int, int> &p2) {
    if (p1.first == p2.first) {
      return p1.second < p2.second;
    } else
      return p1.first > p2.first;
  }
};
long long sub(long long A, long long B) { return (A - B + mod) % mod; }
void toposort(vector<int> &order, int v, int visited[], vector<int> adj[]) {
  visited[v] = 1;
  int i;
  for (i = 0; i < adj[v].size(); i++) {
    if (!visited[adj[v][i]]) {
      toposort(order, adj[v][i], visited, adj);
    }
  }
  order.push_back(v);
}
ll segtree[4 * 200000 + 1];
void build(ll A[], ll tl, ll tr, ll v) {
  if (tl == tr)
    segtree[v] = A[tl];
  else {
    ll tm = (tl + tr) / 2;
    build(A, tl, tm, v * 2);
    build(A, tm + 1, tr, 2 * v + 1);
    segtree[v] = max(segtree[2 * v], segtree[2 * v + 1]);
  }
}
ll maxival(ll v, ll tl, ll tr, ll l, ll r) {
  if (l > r)
    return 0;
  if (l == tl && r == tr)
    return segtree[v];
  ll tm = (tl + tr) / 2;
  return max(maxival(2 * v, tl, tm, l, min(r, tm)),
             maxival(2 * v + 1, tm + 1, tr, max(l, tm + 1), r));
}
void updateval(ll v, ll tl, ll tr, ll pos, ll newval) {
  if (tl == tr)
    segtree[v] = newval;
  else {
    ll tm = (tl + tr) / 2;
    if (pos <= tm)
      updateval(2 * v, tl, tm, pos, newval);
    else
      updateval(2 * v + 1, tm + 1, tr, pos, newval);
    segtree[v] = max(segtree[2 * v], segtree[2 * v + 1]);
  }
}
ll dp[10000 + 2][100 + 1][2];
long long calcdp(string &k, ll d, ll pos, ll rem, ll index) {
  ll i;
  if (index == k.size()) {
    if (rem == 0)
      return 1ll;
    return 0ll;
  }
  if (dp[index][rem][pos] != -1)
    return dp[index][rem][pos];
  dp[index][rem][pos] = 0ll;
  if (pos == 0) {
    for (i = 0; i < k[index] - '0'; i++) {
      dp[index][rem][pos] =
          add(dp[index][rem][pos], calcdp(k, d, 1, (rem + i) % d, index + 1));
    }
    dp[index][rem][pos] =
        add(dp[index][rem][pos], calcdp(k, d, 0, (rem + i) % d, index + 1));
  } else {
    for (i = 0; i <= 9; i++)
      dp[index][rem][pos] =
          add(dp[index][rem][pos], calcdp(k, d, 1, (rem + i) % d, index + 1));
  }
  return dp[index][rem][pos];
}
int main() {

  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cout << fixed << setprecision(10);
  cerr << fixed << setprecision(5);
  int t = 1;
  // SieveOfEratosthenes(100005);
  // precalc();
  // freopen("input.txt","r",stdin);
  // freopen("output.txt","w",stdout);
  // cin>>t;
  while (t--) {
    string k;
    long long d;
    cin >> k >> d;
    memset(dp, -1ll, sizeof(dp));
    cout << (calcdp(k, d, 0, 0, 0) + mod - 1) % mod;
  }
  return 0;
}