Problem p03825 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stdio.h>
#include <utility>
#include <vector>
using namespace std;
#define y0 y0z
#define y1 y1z
#define yn ynz
#define j0 j0z
#define j1 j1z
#define jn jnz
#define tm tmz
#define buli(x) (__builtin_popcountll(x))
#define bur0(x) (__builtin_ctzll(x))
#define bul2(x) (63 - __builtin_clzll(x))
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define fil(a, b) memset((a), (b), sizeof(a))
#define cl(a) fil(a, 0)
#define siz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define foreach(it, a)                                                         \
  for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define rep(i, a, b) for (int i = (a), _ed = (b); i < _ed; i++)
#define per(i, a, b) for (int i = (b)-1, _ed = (a); i >= _ed; i--)
#define forg(i, gu) for (int i = gu; ~i; i = e[i].next)
#define pw(x) ((ll(1)) << (x))
#define upmo(a, b) (((a) = ((a) + (b)) % mo) < 0 ? (a) += mo : (a))
#define mmo(a, b) (((a) = 1ll * (a) * (b) % mo) < 0 ? (a) += mo : (a))
void getre() {
  int x = 0;
  printf("%d\n", 1 / x);
}
void gettle() {
  int res = 1;
  while (1)
    res <<= 1;
  printf("%d\n", res);
}
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpii;
template <typename T, typename S> inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S> inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
template <typename N, typename PN> inline N flo(N a, PN b) {
  return a >= 0 ? a / b : -((-a - 1) / b) - 1;
}
template <typename N, typename PN> inline N cei(N a, PN b) {
  return a > 0 ? (a - 1) / b + 1 : -(-a / b);
}
template <typename N> N gcd(N a, N b) { return b ? gcd(b, a % b) : a; }
template <typename N> inline int sgn(N a) {
  return a > 0 ? 1 : (a < 0 ? -1 : 0);
}
#if ((_WIN32 || __WIN32__) && __cplusplus < 201103L)
#define lld "%I64d"
#else
#define lld "%lld"
#endif
inline void gn(long long &x) {
  int sg = 1;
  char c;
  while (((c = getchar()) < '0' || c > '9') && c != '-')
    ;
  c == '-' ? (sg = -1, x = 0) : (x = c - '0');
  while ((c = getchar()) >= '0' && c <= '9')
    x = x * 10 + c - '0';
  x *= sg;
}
inline void gn(int &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(unsigned long long &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gn(long double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gs(char *s) { scanf("%s", s); }
inline void gc(char &c) {
  while ((c = getchar()) > 126 || c < 33)
    ;
}
inline void pc(char c) { putchar(c); }
#ifdef JCVB
#define debug(...) fprintf(stderr, __VA_ARGS__)
#else
#define debug(...)
#endif
typedef long long ll;
typedef double db;
inline ll sqr(ll a) { return a * a; }
inline db sqrf(db a) { return a * a; }
const int inf = 0x3f3f3f3f;
// const ll inf=0x3f3f3f3f3f3f3f3fll;
const db pi = 3.14159265358979323846264338327950288L;
const db eps = 1e-6;
const int mo = 1e9 + 7;
int qp(int a, ll b) {
  int n = 1;
  do {
    if (b & 1)
      n = 1ll * n * a % mo;
    a = 1ll * a * a % mo;
  } while (b >>= 1);
  return n;
}

int f[2222][4222];
int n, m, k;
int res = 0;
int main() {
#ifdef JCVB
  // freopen("1.in","r",stdin);
  // freopen("1.out","w",stdout);
  int _time_jc = clock();
#endif
  gn(n);
  gn(m);
  gn(k);

  f[0][0] = 1;
  int d = (n + m - 1) / (k - 1);
  d++;
  rep(i, 0, d) rep(j, 0, m + 1) if (f[i][j]) {
    rep(t, 0, k) upmo(f[i + 1][j + t], f[i][j]);
    rep(t, 1, k) {
      int tot = i * (k - 1) + k;
      int tot1 = j + t;
      int tot0 = tot - tot1;
      if (tot1 <= m && tot0 <= n && (n - tot0) % (k - 1) == 0)
        upmo(res, f[i][j]);
    }
  }
  printf("%d\n", res);
#ifdef JCVB
  debug("time: %d\n", int(clock() - _time_jc));
#endif
  return 0;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stdio.h>
#include <utility>
#include <vector>
using namespace std;
#define y0 y0z
#define y1 y1z
#define yn ynz
#define j0 j0z
#define j1 j1z
#define jn jnz
#define tm tmz
#define buli(x) (__builtin_popcountll(x))
#define bur0(x) (__builtin_ctzll(x))
#define bul2(x) (63 - __builtin_clzll(x))
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define fil(a, b) memset((a), (b), sizeof(a))
#define cl(a) fil(a, 0)
#define siz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define foreach(it, a)                                                         \
  for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define rep(i, a, b) for (int i = (a), _ed = (b); i < _ed; i++)
#define per(i, a, b) for (int i = (b)-1, _ed = (a); i >= _ed; i--)
#define forg(i, gu) for (int i = gu; ~i; i = e[i].next)
#define pw(x) ((ll(1)) << (x))
#define upmo(a, b) (((a) = ((a) + (b)) % mo) < 0 ? (a) += mo : (a))
#define mmo(a, b) (((a) = 1ll * (a) * (b) % mo) < 0 ? (a) += mo : (a))
void getre() {
  int x = 0;
  printf("%d\n", 1 / x);
}
void gettle() {
  int res = 1;
  while (1)
    res <<= 1;
  printf("%d\n", res);
}
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpii;
template <typename T, typename S> inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S> inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
template <typename N, typename PN> inline N flo(N a, PN b) {
  return a >= 0 ? a / b : -((-a - 1) / b) - 1;
}
template <typename N, typename PN> inline N cei(N a, PN b) {
  return a > 0 ? (a - 1) / b + 1 : -(-a / b);
}
template <typename N> N gcd(N a, N b) { return b ? gcd(b, a % b) : a; }
template <typename N> inline int sgn(N a) {
  return a > 0 ? 1 : (a < 0 ? -1 : 0);
}
#if ((_WIN32 || __WIN32__) && __cplusplus < 201103L)
#define lld "%I64d"
#else
#define lld "%lld"
#endif
inline void gn(long long &x) {
  int sg = 1;
  char c;
  while (((c = getchar()) < '0' || c > '9') && c != '-')
    ;
  c == '-' ? (sg = -1, x = 0) : (x = c - '0');
  while ((c = getchar()) >= '0' && c <= '9')
    x = x * 10 + c - '0';
  x *= sg;
}
inline void gn(int &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(unsigned long long &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gn(long double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gs(char *s) { scanf("%s", s); }
inline void gc(char &c) {
  while ((c = getchar()) > 126 || c < 33)
    ;
}
inline void pc(char c) { putchar(c); }
#ifdef JCVB
#define debug(...) fprintf(stderr, __VA_ARGS__)
#else
#define debug(...)
#endif
typedef long long ll;
typedef double db;
inline ll sqr(ll a) { return a * a; }
inline db sqrf(db a) { return a * a; }
const int inf = 0x3f3f3f3f;
// const ll inf=0x3f3f3f3f3f3f3f3fll;
const db pi = 3.14159265358979323846264338327950288L;
const db eps = 1e-6;
const int mo = 1e9 + 7;
int qp(int a, ll b) {
  int n = 1;
  do {
    if (b & 1)
      n = 1ll * n * a % mo;
    a = 1ll * a * a % mo;
  } while (b >>= 1);
  return n;
}

int f[4222][4222];
int n, m, k;
int res = 0;
int main() {
#ifdef JCVB
  // freopen("1.in","r",stdin);
  // freopen("1.out","w",stdout);
  int _time_jc = clock();
#endif
  gn(n);
  gn(m);
  gn(k);

  f[0][0] = 1;
  int d = (n + m - 1) / (k - 1);
  d++;
  rep(i, 0, d) rep(j, 0, m + 1) if (f[i][j]) {
    rep(t, 0, k) upmo(f[i + 1][j + t], f[i][j]);
    rep(t, 1, k) {
      int tot = i * (k - 1) + k;
      int tot1 = j + t;
      int tot0 = tot - tot1;
      if (tot1 <= m && tot0 <= n && (n - tot0) % (k - 1) == 0)
        upmo(res, f[i][j]);
    }
  }
  printf("%d\n", res);
#ifdef JCVB
  debug("time: %d\n", int(clock() - _time_jc));
#endif
  return 0;
}