Submission #127552

#	Time	Username	Problem	Language	Result	Execution time	Memory
127552		RockyB	Tents (JOI18_tents)	C++17	100 / 100	136 ms	35704 KiB

tents

#include <bits/stdc++.h>
 
#define rep(a, b, c) for (int a = (b); (a) <= (c); a++)
#define per(a, b, c) for (int a = (b); (a) >= (c); a--)
 
#define nl '\n'
#define ioi exit(0);
 
const int mod = (int)1e9 + 7;
const int N = (int)1e4;
 
using namespace std;
 
void add(int &x, int y) {
  x += y;
  if (x >= mod) x -= mod;
}
int sum(int x, int y) {
  add(x, y);
  return x;
}
int n, m;
 
int dp[3005][3005];
int main() {
  #ifdef IOI
    freopen ("in.txt", "r", stdin);
    freopen ("slow.out", "w", stdout);
  #endif
  cin >> n >> m;
  /* memset(dp, -1, sizeof(dp));
  int ans = sum(calc(), -1);
  cout << ans << nl; */
  dp[0][m] = 1;
  rep(i, 0, n - 1) {
    rep(j, 0, m) {
      add(dp[i + 1][j], dp[i][j]);
      if (j > 0) {
        add(dp[i + 1][j - 1], dp[i][j] * 1ll * 4 * j % mod);
      	add(dp[i + 2][j - 1], dp[i][j] * 1ll * (n - i - 1) * j % mod);
      }
      if (j > 1) add(dp[i + 1][j - 2], dp[i][j] * 1ll * (j * (j - 1) / 2) % mod);
    }
  }
  int ans = -1;
  rep(i, 0, m) add(ans, dp[n][i]);
  if (ans < 0) ans += mod;
  cout << ans;
  ioi
}
 
/*
 
5116 0
3720 1
450 2
 
*/

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