Submission #828866

#	Time	Username	Problem	Language	Result	Execution time	Memory
828866		MohamedAhmed04	Asceticism (JOI18_asceticism)	C++14	100 / 100	12 ms	1124 KiB

asceticism

#include <bits/stdc++.h>

using namespace std ;

const int mod = 1e9 + 7 ;

int Add(int x , int y)
{
	int z = x + y ;
	if(z >= mod)
		z -= mod ;
	return z ;
}

int Sub(int x , int y)
{
	int z = x - y ;
	if(z < 0)
		z += mod ;
	return z ;
}

int Mul(int x , int y)
{
	return (x * 1ll * y) % mod ;
}

int powlog(int base , int power)
{
	if(power == 0)
		return 1 ;
	int x = powlog(base , power / 2) ;
	x = Mul(x , x) ;
	if(power & 1)
		x = Mul(x , base) ;
	return x ;
}

int modinv(int x)
{
	return powlog(x , mod-2) ;
}

int Div(int x , int y)
{
	return Mul(x , modinv(y)) ;
}

struct combination
{
    vector<int>fact , inv ;
    combination(int sz) : fact(sz + 1) , inv(sz + 1)
    {
        fact[0] = 1 ;
        inv[0] = 1 ;
        for(int i = 1 ; i <= sz ; ++i)
            fact[i] = Mul(fact[i-1] , i) ;
        inv[sz] = modinv(fact[sz]) ;
		for(int i = sz-1 ; i >= 1 ; --i)
		    inv[i] = Mul(inv[i+1] , i+1) ;
    }
    int choose(int n , int k) const
    {
        if(k < 0 || n < k)
            return 0 ;
        return Mul(Mul(fact[n] , inv[k]) , inv[n - k]) ;
    }
};

const int MAX = 1e5 + 10 ;

combination comb(MAX) ;

int arr[MAX] ;
int n , k ;

int main()
{
	ios_base::sync_with_stdio(0) ;
	cin.tie(0) ;
	cin>>n>>k ;
	k = n-k ;
	int ans = 0 ;
	for(int i = 0 ; i <= k ; ++i)
	{
		int x = Mul(comb.choose(n+1 , i) , powlog(k+1-i , n)) ;
		if(i%2 == 0)
			ans = Add(ans , x) ;
		else
			ans = Sub(ans , x) ;
	}
	return cout<<ans<<"\n" , 0 ;
}		

• Subtask 1: 4 / 4
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 51 / 51