Submission #114109

#	Time	Username	Problem	Language	Result	Execution time	Memory
114109		shayan_p	Asceticism (JOI18_asceticism)	C++14	49 / 100	1068 ms	1368 KiB

asceticism

// High above the clouds there is a rainbow...

#include<bits/stdc++.h>

#define F first
#define S second
#define PB push_back
#define sz(s) int((s).size())
#define bit(n,k) (((n)>>(k))&1)

using namespace std;

typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

const int maxn=1e5+10,mod=1e9+7;
const ll inf=1e18;

int dp[maxn],fac[maxn],ifac[maxn],dp2[maxn];

int Pow(int a,int b){
    int ans=1;
    for(;b;b>>=1,a=1ll*a*a %mod){
	if(b&1) ans=1ll*ans*a %mod;
    }
    return ans;
}
int C(int n,int k){
    return 1ll*fac[n] * ifac[k] %mod *ifac[n-k] %mod;
}

int main(){
    ios_base::sync_with_stdio(false);cin.tie(0);
    fac[0]=1;
    for(int i=1;i<maxn;i++)
	fac[i]=1ll*i*fac[i-1] %mod;
    ifac[maxn-1]=Pow(fac[maxn-1],mod-2);
    for(int i=maxn-2;i>=0;i--)
	ifac[i]=1ll*(i+1)*ifac[i+1] %mod;
    int n,k;cin>>n>>k;
    for(int i=1;i<=k;i++){
	dp2[i]=1ll*Pow(i,n);
	for(int j=1;j<i;j++)
	    dp2[i]=(dp2[i]-1ll*dp2[j]*C(i,j))%mod;
	dp[i]=dp2[i];
	for(int j=1;j<i;j++)
	    dp[i]=(dp[i]-1ll*dp[j]*C(n-j,i-j))%mod;
    }
    if(dp[k]<0) dp[k]+=mod;
    return cout<<dp[k]<<endl,0;
}
// Deathly mistakes:
//  * Read the problem curfully.
//  * Check maxn.
//  * Overflows.

• Subtask 1: 4 / 4
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 0 / 51