Submission #1210749

#	Time	Username	Problem	Language	Result	Execution time	Memory
1210749		boss_zz	Tents (JOI18_tents)	C++20	100 / 100	97 ms	70980 KiB

tents

#include<bits/stdc++.h>
#define rep(a,b,c) for(ll a=b;a<=c;++a)
#define ll long long 
#define ff first 
#define ss second 
#define mp make_pair 
using namespace std;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
const ll N=3005,inf=1e18,mod=1e9+7;
ll n,m,dp[N][N],fac[N],inv[N];
ll fpow(ll a,ll b){
    ll res=1;
    while(b){
        if(b&1) (res*=a)%=mod;
        (a*=a)%=mod;
        b>>=1;
    }
    return res;
}
void build(){
    fac[0]=1;
    rep(i,1,N-5) (fac[i]=fac[i-1]*i)%=mod;
    inv[N-5]=fpow(fac[N-5],mod-2);
    for(ll i=N-6;i>=0;--i) (inv[i]=inv[i+1]*(i+1))%=mod;
}
ll C(ll n,ll k)
{return fac[n]*inv[k]%mod*inv[n-k]%mod;}
signed main(){
    ios::sync_with_stdio(0);cin.tie(0);
    cin>>n>>m;
    build();
    dp[0][0]=1;
    rep(i,1,n) dp[i][0]=1;
    rep(i,1,m) dp[0][i]=1;
    rep(i,1,n){
        rep(j,1,m){
            dp[i][j]+=dp[i-1][j];
            (dp[i][j]+=dp[i-1][j-1]*j*4)%=mod;
            if(i>1) (dp[i][j]+=dp[i-2][j-1]*(i-1)*j)%=mod;
            if(j>1) (dp[i][j]+=dp[i-1][j-2]*C(j,2))%=mod;
        }
    }
    cout<<(dp[n][m]-1+mod)%mod<<'\n';
    return 0;
}

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