Submission #3225926

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Source Code Expand

/*#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")*/
#include<bits/stdc++.h>
#define ll long long
#define inf 1000000005
#define mod 1000000007
#define put putchar('\n')
#define F(i,a,b) for (int i=(a);i<=(b);i++)
#define D(i,a,b) for (int i=(a);i>=(b);i--)
#define go(i,t) for (int i=head[t];i;i=Next[i])
#define sqr(x) ((x)*(x))
#define re register
#define mp make_pair
#define fi first
#define se second
#define pa pair<int,int>
#define pb push_back
#define be begin()
#define en end()
#define ret return puts("-1"),0;
#define N 1000055
//#define int ll
using namespace std;
inline char gc(){
    static char buf[100000],*p1=buf,*p2=buf;
    return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;
}
#define gc getchar
inline int read(){char c=getchar();int tot=1;while ((c<'0'|| c>'9')&&c!='-') c=getchar();if (c=='-'){tot=-1;c=getchar();}
int sum=0;while (c>='0'&&c<='9'){sum=sum*10+c-'0';c=getchar();}return sum*tot;}
inline void wr(int x){if (x<0) {putchar('-');wr(-x);return;}if(x>=10)wr(x/10);putchar(x%10+'0');}
inline void wrn(int x){wr(x);put;}inline void wri(int x){wr(x);putchar(' ');}
inline void wrn(int x,int y){wri(x);wrn(y);}inline void wrn(int a,int b,int c){wri(a);wrn(b,c);}
int n,m,fac[N],inv[N],f[N],ans;
int C(int n,int m){
	if (n<m||m<0) return 0;
	return (ll) fac[n]*inv[n-m]%mod;
}
int ksm(int x,int k){
	int sum=1;
	while (k){
		if (k&1) sum=(ll)sum*x%mod;
		x=(ll)x*x%mod;
		k>>=1;
	}
	return sum;
}
signed main(){
	n=read();
	fac[0]=1;F(i,1,n) fac[i]=(ll)fac[i-1]*i%mod;
	inv[n]=ksm(fac[n],mod-2);D(i,n-1,0) inv[i]=(ll)inv[i+1]*(i+1)%mod;
	F(i,(n+1)/2,n-1){
		f[i]=(ll)C(i-1,n-i-1)*fac[i]%mod;
		ans=(ans+(ll)(f[i]-f[i-1])*i)%mod;
	}
	wrn((ans+mod)%mod);
	return 0;
}

Submission Info

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