Problem p02738 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <vector>
#define N ()
#define M ()
#define inf (0x7f7f7f7f)
#define rg register int
#define Label puts("NAIVE")
#define spa print(' ')
#define ent print('\n')
#define rand() (((rand()) << (15)) ^ (rand()))
#define file(s) freopen(s ".in", "r", stdin), freopen(s ".out", "w", stdout)
typedef long double ld;
typedef long long LL;
typedef unsigned long long ull;
using namespace std;
namespace fastIO1 {
inline char read() {
  static const int IN_LEN = 1000000;
  static char buf[IN_LEN], *s, *t;
  return (s == t               ? t = (s = buf) + fread(buf, 1, IN_LEN, stdin),
          (s == t ? -1 : *s++) : *s++);
}
template <class T> inline void read(T &x) {
  static bool iosig;
  static char c;
  for (iosig = false, c = read(); !isdigit(c); c = read()) {
    if (c == '-')
      iosig = true;
    if (c == -1)
      return;
  }
  for (x = 0; isdigit(c); c = read())
    x = ((x + (x << 2)) << 1) + (c ^ '0');
  if (iosig)
    x = -x;
}
inline char readc(char &c) {
  for (c = read(); !isalpha(c) && !isdigit(c); c = read())
    if (c == -1)
      return 0;
}
const int OUT_LEN = 10000000;
char obuf[OUT_LEN], *ooh = obuf;
inline void print(char c) {
  if (ooh == obuf + OUT_LEN)
    fwrite(obuf, 1, OUT_LEN, stdout), ooh = obuf;
  *ooh++ = c;
}
template <class T> inline void print(T x) {
  static int buf[30], cnt;
  if (x == 0)
    print('0');
  else {
    if (x < 0)
      print('-'), x = -x;
    for (cnt = 0; x; x /= 10)
      buf[++cnt] = x % 10 + 48;
    while (cnt)
      print((char)buf[cnt--]);
  }
}
inline void flush() { fwrite(obuf, 1, ooh - obuf, stdout); }
} // namespace fastIO1
namespace fastIO2 {
template <class T> inline void read(T &x) {
  static bool iosig;
  static char c;
  for (iosig = false, c = getchar(); !isdigit(c); c = getchar()) {
    if (c == '-')
      iosig = true;
    if (c == -1)
      return;
  }
  for (x = 0; isdigit(c); c = getchar())
    x = ((x + (x << 2)) << 1) + (c ^ '0');
  if (iosig)
    x = -x;
}
} // namespace fastIO2
using namespace fastIO1;
int n, P, f[1210][1610], ans;
void add(int &x, int y) { x = x + y > P ? x + y - P : x + y; }
int main() {
  read(n);
  read(P);
  f[0][n] = 1;
  for (int i = 1; i <= 3 * n; i++)
    for (int j = -n; j <= 3 * n; j++) {
      if (j + n > 0)
        add(f[i][j + n], f[i - 1][j - 1 + n]);
      if (i >= 2)
        add(f[i][j + n], 1ll * (i - 1) * f[i - 2][j + 1 + n] % P);
      if (i >= 3)
        add(f[i][j + n], 1ll * (i - 1) * (i - 2) % P * f[i - 3][j + n] % P);
    }
  for (int i = n; i <= 4 * n; i += 3)
    add(ans, f[n * 3][i]);
  printf("%d\n", ans);
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <vector>
#define N ()
#define M ()
#define inf (0x7f7f7f7f)
#define rg register int
#define Label puts("NAIVE")
#define spa print(' ')
#define ent print('\n')
#define rand() (((rand()) << (15)) ^ (rand()))
#define file(s) freopen(s ".in", "r", stdin), freopen(s ".out", "w", stdout)
typedef long double ld;
typedef long long LL;
typedef unsigned long long ull;
using namespace std;
namespace fastIO1 {
inline char read() {
  static const int IN_LEN = 1000000;
  static char buf[IN_LEN], *s, *t;
  return (s == t               ? t = (s = buf) + fread(buf, 1, IN_LEN, stdin),
          (s == t ? -1 : *s++) : *s++);
}
template <class T> inline void read(T &x) {
  static bool iosig;
  static char c;
  for (iosig = false, c = read(); !isdigit(c); c = read()) {
    if (c == '-')
      iosig = true;
    if (c == -1)
      return;
  }
  for (x = 0; isdigit(c); c = read())
    x = ((x + (x << 2)) << 1) + (c ^ '0');
  if (iosig)
    x = -x;
}
inline char readc(char &c) {
  for (c = read(); !isalpha(c) && !isdigit(c); c = read())
    if (c == -1)
      return 0;
}
const int OUT_LEN = 10000000;
char obuf[OUT_LEN], *ooh = obuf;
inline void print(char c) {
  if (ooh == obuf + OUT_LEN)
    fwrite(obuf, 1, OUT_LEN, stdout), ooh = obuf;
  *ooh++ = c;
}
template <class T> inline void print(T x) {
  static int buf[30], cnt;
  if (x == 0)
    print('0');
  else {
    if (x < 0)
      print('-'), x = -x;
    for (cnt = 0; x; x /= 10)
      buf[++cnt] = x % 10 + 48;
    while (cnt)
      print((char)buf[cnt--]);
  }
}
inline void flush() { fwrite(obuf, 1, ooh - obuf, stdout); }
} // namespace fastIO1
namespace fastIO2 {
template <class T> inline void read(T &x) {
  static bool iosig;
  static char c;
  for (iosig = false, c = getchar(); !isdigit(c); c = getchar()) {
    if (c == '-')
      iosig = true;
    if (c == -1)
      return;
  }
  for (x = 0; isdigit(c); c = getchar())
    x = ((x + (x << 2)) << 1) + (c ^ '0');
  if (iosig)
    x = -x;
}
} // namespace fastIO2
using namespace fastIO1;
int n, P, f[6010][8010], ans;
void add(int &x, int y) { x = x + y > P ? x + y - P : x + y; }
int main() {
  read(n);
  read(P);
  f[0][n] = 1;
  for (int i = 1; i <= 3 * n; i++)
    for (int j = -n; j <= 3 * n; j++) {
      if (j + n > 0)
        add(f[i][j + n], f[i - 1][j - 1 + n]);
      if (i >= 2)
        add(f[i][j + n], 1ll * (i - 1) * f[i - 2][j + 1 + n] % P);
      if (i >= 3)
        add(f[i][j + n], 1ll * (i - 1) * (i - 2) % P * f[i - 3][j + n] % P);
    }
  for (int i = n; i <= 4 * n; i += 3)
    add(ans, f[n * 3][i]);
  printf("%d\n", ans);
}