Submission #1227854

#	Time	Username	Problem	Language	Result	Execution time	Memory
1227854		_rain_	Tents (JOI18_tents)	C++20	100 / 100	86 ms	35652 KiB

tents

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;

const int MOD=(int)1e9+7;
	int add(int a,int b){
		return a+b>=MOD?a+b-MOD:a+b;
	}
	int sub(int a,int b){
		return a-b<0?a-b+MOD:a-b;
	}
	int mul(int a,int b){
		return (LL)a*b%MOD;
	}
	int power(int a,int b){
		int res=1;
		for(;b;b>>=1,a=mul(a,a)){
			if (b&1) res=mul(res,a);
		}
		return res;
	}
	
	
const int N=(int)3000;
	int fac[N+2] , inv[N+2];
	
	void build(){
		fac[0]=1;
		for(int i=1;i<=N;++i) fac[i]=mul(fac[i-1],i);
		inv[N]=power(fac[N],MOD-2);
		for(int i=N;i>=1;--i) inv[i-1]=mul(inv[i],i);
		return;
	}
	int C(int x,int y){
		if (x>y) return 0;
		return (LL)fac[y]*inv[y-x]%MOD*inv[x]%MOD;
	}
	
	int numrow,numcol;
	int f[N+2][N+2];

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0) ; cout.tie(0);
	#define task "main"
	if (fopen(task".inp","r")){
		freopen(task".inp","r",stdin);
		freopen(task".out","w",stdout);
	}
	
	cin>>numrow>>numcol;
	build();
	for(int i=0;i<=max(numrow,numcol);++i) f[i][0]=f[0][i]=1;
	for(int i=1;i<=numrow;++i){
		for(int j=1;j<=numcol;++j){
			f[i][j]=mul(f[i-1][j-1],mul(4,i));
			f[i][j]=add(f[i][j],f[i][j-1]);
			if (i>=2){
				f[i][j]=add(f[i][j],mul(C(2,i),f[i-2][j-1]));
			}
			if (j>=2){
				f[i][j]=add(f[i][j],mul(mul(i,j-1),f[i-1][j-2]));
			}
		}
	}
	cout<<sub(f[numrow][numcol],1);
	
	return 0;
}

Compilation message (stderr)

tents.cpp: In function 'int main()':
tents.cpp:47:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   47 |                 freopen(task".inp","r",stdin);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
tents.cpp:48:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   48 |                 freopen(task".out","w",stdout);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

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