Submission #171940

#	Time	Username	Problem	Language	Result	Execution time	Memory
171940		arnold518	Asceticism (JOI18_asceticism)	C++14	100 / 100	21 ms	2040 KiB

asceticism

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

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

const int MAXN = 1e5;
const ll MOD = 1e9+7;

int N, K;

ll mypow(ll x, ll y)
{
    if(y==0) return 1;
    if(y%2) return mypow(x, y-1)*x%MOD;
    ll t=mypow(x, y/2);
    return t*t%MOD;
}

ll inv(ll x) { return mypow(x, MOD-2); }

ll fact[MAXN+10], invfact[MAXN+10];

ll comb(ll n, ll r) { return fact[n]*invfact[r]%MOD*invfact[n-r]%MOD; }

int main()
{
    int i, j;

    scanf("%d%d", &N, &K);

    fact[0]=1;
    for(i=1; i<=N+5; i++) fact[i]=fact[i-1]*i%MOD;

    invfact[N+5]=inv(fact[N+5]);
    for(i=N+5; i>=1; i--) invfact[i-1]=invfact[i]*i%MOD;


    ll ans=0;
    for(i=0; i<=K; i++)
    {
        if(i%2) ans-=mypow(K-i, N)*comb(N+1, i)%MOD;
        else ans+=mypow(K-i, N)*comb(N+1, i)%MOD;
        ans%=MOD;
        ans+=MOD;
        ans%=MOD;
    }
    printf("%lld", ans);
}

Compilation message (stderr)

asceticism.cpp: In function 'int main()':
asceticism.cpp:29:12: warning: unused variable 'j' [-Wunused-variable]
     int i, j;
            ^
asceticism.cpp:31:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d", &N, &K);
     ~~~~~^~~~~~~~~~~~~~~~

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