Submission #198252

#	Time	Username	Problem	Language	Result	Execution time	Memory
198252		quocnguyen1012	Tents (JOI18_tents)	C++14	100 / 100	287 ms	35832 KiB

tents

#include <bits/stdc++.h>

#define fi first
#define se second
#define mp make_pair
#define pb push_back

using namespace std;
typedef long long ll;

const int maxn = 3e3 + 5, mod = 1e9 + 7;

void add(int & a, int b)
{
  a += b;
  if (a >= mod) a -= mod;
  if (a < 0) a += mod;
}

int mul(int a, int b)
{
  return 1ll * a * b % mod;
}

int N, M;
int f[maxn][maxn];

signed main(void)
{
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  if (fopen("A.INP", "r")){
    freopen("A.INP", "r", stdin);
    freopen("A.OUT", "w", stdout);
  }
  cin >> N >> M;
  for (int i = 0; i < maxn; ++i)
    f[i][0] = 1, f[0][i] = 1;
  for (int i = 1; i <= N; ++i){
    for (int j = 1; j <= M; ++j){
      int & res = f[i][j];
      add(res,f[i - 1][j]);
      add(res,mul(f[i - 1][j - 1],4 * j));
      if (i > 1)  add(res,mul(f[i - 2][j - 1],j * (i - 1)));
      if (j > 1)  add(res,mul(f[i - 1][j - 2],j * (j - 1) / 2));
    }
  }
  add(f[N][M], -1);
  cout << f[N][M] << '\n';
}

Compilation message (stderr)

tents.cpp: In function 'int main()':
tents.cpp:32:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
     freopen("A.INP", "r", stdin);
     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
tents.cpp:33:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
     freopen("A.OUT", "w", stdout);
     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 48 / 48
• Subtask 2: 52 / 52