Submission #1034135

#	Time	Username	Problem	Language	Result	Execution time	Memory
1034135		anHiep	Tents (JOI18_tents)	C++14	100 / 100	221 ms	71244 KiB

tents

#include <bits/stdc++.h>
 
using namespace std;
 
const int mod = 1e9 + 7;

#define int long long
 
int dp[3003][3003];
int dv;
 
int bp(int a, int b){
    if(b == 0) return 1;
    if(b == 1) return a;
    int k = bp(a, b/2);
    k = (k * k) % mod;
    if(b % 2 == 0) return k;
    return (a * k) % mod;
}
 
int cal(int i, int j){
    if(i < 0 || j < 0) return 0;
    if(dp[i][j] != -1) return dp[i][j];
    int ans = 0;
    ans = (ans + cal(i - 1, j)) % mod;
    ans = (ans + cal(i - 1, j - 2) * j % mod * (j - 1) % mod * dv % mod) % mod;
    ans = (ans + cal(i - 2, j - 1) * j % mod * (i - 1) % mod) % mod;
    ans = (ans + cal(i - 1, j - 1) * j % mod * 4 % mod) % mod;
 
    return dp[i][j] = ans;
}
 
signed main(){
    int n, m;
    cin >> n >> m;
    dv = bp(2, mod - 2);
    for(int i = 0; i <= n; i++) for(int j = 0; j <= m; j++) dp[i][j] = -1;
    for(int i = 0; i <= n; i++) dp[i][0] = 1;
    for(int i = 0; i <= m; i++) dp[0][i] = 1;
    cout << (cal(n, m) - 1 + mod)%mod;
    return 0;
}

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