Submission #132328

#	Time	Username	Problem	Language	Result	Execution time	Memory
132328		duality	Tents (JOI18_tents)	C++11	100 / 100	218 ms	70904 KiB

tents

#include <bits/stdc++.h>
using namespace std;
#define mp make_pair
#define pb push_back
typedef long long int LLI;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef vector<pii> vpii;
#define MOD 1000000007

LLI inv(LLI n) {
    int e = MOD-2;
    LLI r = 1;
    while (e > 0) {
        if (e & 1) r *= n,r %= MOD;
        e >>= 1;
        n *= n,n %= MOD;
    }
    return r;
}
LLI fact[3001],invf[3001],invpow2[6001];
LLI dp[3001][3001];
LLI choose(LLI n,LLI k) {
    return (fact[n]*((invf[k]*invf[n-k]) % MOD)) % MOD;
}
int main() {
    int H,W;
    cin >> H >> W;

    int i,j;
    LLI ans = 0;
    fact[0] = invf[0] = 1;
    for (i = 1; i <= max(H,W); i++) fact[i] = (fact[i-1]*i) % MOD,invf[i] = inv(fact[i]);
    invpow2[0] = 1;
    for (i = 1; i <= H+W; i++) invpow2[i] = (invpow2[i-1]*inv(2)) % MOD;
    for (i = 0; i <= W; i++) dp[0][i] = 1;
    for (i = 1; i <= H; i++) {
        dp[i][0] = 1;
        for (j = 1; j <= W; j++) dp[i][j] = (dp[i-1][j]+4*j*dp[i-1][j-1]) % MOD;
    }
    for (i = 0; i <= H; i++) {
        for (j = 0; j <= W; j++) {
            if ((i+2*j <= H) && (j+2*i <= W)) {
                LLI x = (((choose(H,i)*choose(W,2*i)) % MOD)*fact[2*i]) % MOD;
                LLI y = (((choose(W-2*i,j)*choose(H-i,2*j)) % MOD)*fact[2*j]) % MOD;
                ans += ((x*y) % MOD)*((dp[H-i-2*j][W-j-2*i]*invpow2[i+j]) % MOD);
                ans %= MOD;
            }
        }
    }
    cout << (ans+MOD-1) % MOD << endl;

    return 0;
}

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