Submission #127484

#	Time	Username	Problem	Language	Result	Execution time	Memory
127484		RockyB	Tents (JOI18_tents)	C++17	100 / 100	367 ms	35836 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;
  if (x < 0) x += mod;
}
int sum(int x, int y) {
  add(x, y);
  return x;
}
int n, m;

int dp[3001][3001];
int calc(int v = n, int free = m) {
  if (!v) return 1;
  if (~dp[v][free]) return dp[v][free];
  int res = calc(v - 1, free);
  // put < or > or ^ or v
  if (free > 0) {
    add(res, calc(v - 1, free - 1) * 1ll * free * 4 % mod);
    // connect v and ^
    if (v > 1) add(res, calc(v - 2, free - 1) * 1ll * (v - 1) * free % mod);
  }
  // connect > and <
  if (free > 1) add(res, calc(v - 1, free - 2) * 1ll * (free * (free - 1) / 2) % mod);
  return dp[v][free] = res;
}
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;
  ioi
}

/*

5116 0
3720 1
450 2

*/

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