Submission #752630

#	Time	Username	Problem	Language	Result	Execution time	Memory
752630		bgnbvnbv	Asceticism (JOI18_asceticism)	C++14	100 / 100	14 ms	3452 KiB

asceticism

#include<bits/stdc++.h>
#define TASKNAME "codeforce"
#define pb push_back
#define pli pair<int,int>
#define fi first
#define se second
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL);
using namespace std;
using ll=long long;
const ll maxN=2e5+10;
const ll inf=1e18;
const ll mod=1e9+7;
ll f[maxN],fr[maxN];
ll pw(ll x,ll y)
{
    if(y==0) return 1;
    ll x1=pw(x,y/2);
    x1=x1*x1%mod;
    if(y&1) x1=x1*x%mod;
    return x1;
}
ll C(ll x,ll y)
{
    return f[x]*fr[x-y]%mod*fr[y]%mod;
}
ll n,k,ans=0;
void solve()
{
    cin >> n >> k;
    f[0]=1;
    k--;
    for(int i=1;i<=2*n;i++)
    {
        f[i]=f[i-1]*i%mod;
    }
    fr[2*n]=pw(f[2*n],mod-2);
    for(int i=2*n-1;i>=0;i--)
    {
        fr[i]=fr[i+1]*(i+1)%mod;
    }
    for(int j=0;j<=k+1;j++)
    {
        ll sig=1;
        if(j%2) sig=-1;
        ans+=sig*C(n+1,j)%mod*pw(k-j+1,n)%mod;
        ans%=mod;
    }
    if(ans<0) ans+=mod;
    cout << ans;
}
int main()
{
    fastio
    //freopen(TASKNAME".INP","r",stdin);
    //freopen(TASKNAME".OUT","w",stdout);
    solve();
}

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