Submission #981053

#	Time	Username	Problem	Language	Result	Execution time	Memory
981053		underwaterkillerwhale	Tents (JOI18_tents)	C++17	100 / 100	174 ms	74740 KiB

tents

#include <bits/stdc++.h>
#define se              second
#define fs              first
#define pb              push_back
#define ll              long long
#define ii              pair<ll,ll>
#define ld              long double
#define SZ(v)           (int)v.size()
#define ALL(v)          v.begin(), v.end()
#define bit(msk, i)     ((msk >> i) & 1)
#define iter(id, v)     for(auto id : v)
#define rep(i,m,n)      for(int i=(m); i<=(n); i++)
#define reb(i,m,n)      for(int i=(m); i>=(n); i--)

using namespace std;

mt19937_64 rd(chrono :: steady_clock :: now().time_since_epoch().count());
ll Rand(ll l, ll r) { return uniform_int_distribution<ll> (l, r)(rd); }

const int N = 3e3 + 7;
const ll Mod = 1e9 + 7;
const int szBL = 916;
const ll INF = 1e9;
const int BASE = 137;

int n, m;
ll dp[N][N], f[N][N];
ll fac[(int)1e5 + 7];

ll power (ll n, ll m) {
    if (m == 0) return 1;
    ll t = power(n, m >> 1);
    (t *= t) %= Mod;
    if (m & 1) (t *= n % Mod) %= Mod;
    return t;
}


ll C (int r, int n) {
    if (r > n) return 0;
    return fac[n] * power (fac[r], Mod - 2) % Mod * power (fac[n - r], Mod - 2) % Mod;
}

void fac_init () {
    fac[0] = 1;
    rep (i, 1, 1e5) fac[i] = fac[i - 1] * i % Mod;
}

void solution () {
    fac_init();
     cin >> n >> m;
     dp[0][m] = 1;
     rep (i, 1, n) {
         rep (j, 0, m) {
            (dp[i][j] += dp[i - 1][j + 1] * (j + 1) %Mod * 4 % Mod) %= Mod;
            if (j + 2 <= m) (dp[i][j] += dp[i - 1][j + 2] * ((1LL * (j + 2) * (j + 1) / 2) % Mod) % Mod) %= Mod;
            if (i - 2 >= 0 && j + 1 <= m) (dp[i][j] += dp[i - 2][j + 1] * (i - 1) % Mod * (j + 1) % Mod) %= Mod;
         }
     }
    ll res = 0;
     rep (i, 0, n) {
         ll delta = C(i, n);
         rep (j, 0, m) {
                (res += dp[i][j] * delta % Mod ) %= Mod;
        }
     }
     cout << res - 1<<"\n";
}



#define file(name) freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout);

int main () {
//    file("c");
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    ll num_Test = 1;
//    cin >> num_Test;
    while(num_Test--)
        solution();
}
/*
18 3
2 5
6 21
13 19
9 17
14 17
19 20
2 16
2 10
9 14
19 20
14 16
1 3
17 19
14 21
18 19
4 7
5 12
1 13

*/

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