Submission #20151

#	Time	Username	Problem	Language	Result	Execution time	Memory
20151		tonyjjw	괄호 (kriii4_R)	C++14	8 / 100	291 ms	16904 KiB

R

//*
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<algorithm>
#include<vector>
#define all(A) (A).begin(), (A).end()
  
using namespace std;
  
typedef long long ll;
typedef pair<int,int> pii;
  
const int MN = 1000000+10;
const ll mod = 1000000007;
  
ll fact[MN];
ll inv[MN];
  
ll pow(ll a,ll p){
    ll r=1;
    while(p>0){
        if(p&1)r=r*a%mod;
        a=a*a%mod;
        p>>=1;
    }
    return r;
}
  
ll comb(ll n,ll r){
    return fact[n]*inv[r]%mod*inv[n-r]%mod;
}
ll inverse(ll a){
    return pow(a,mod-2);
}
  
int main(){
    int N,K;
    scanf("%d%d",&N,&K);
    fact[0]=1;
    for(int i=1;i<MN;i++){
        fact[i]=fact[i-1]*i%mod;
    }
    for(int i=0;i<MN;i++){
        inv[i]=inverse(fact[i]);
    }
    ll ans=0;
    for(int i=0;2*i<=N;i++){
        ll v;
        if(i==0){
            v=1;
        }
        else{
            v=comb(N,i)-comb(N,i-1);
        }
        v*=pow(K,N-i);
        v%=mod;
        ans+=v;
        ans%=mod;
    }
    if(ans<0)ans+=mod;
    printf("%lld\n",ans);
    return 0;
}
//*/

• Subtask 1: 8 / 8
• Subtask 2: 0 / 92