CF1349F2. Slime and Sequences (Hard Version)

一个合法正整数序列,满足:对于每个在序列中出现过的数(k),满足(k-1)在最后一个(k)前出现过。

对于每个(k),统计在所有序列中(k)出现的总次数。

(nle 10^5)


首先有个神仙转化:

记二元组((val,pos))表示值为(val),在(pos)位置出现。对其以(val)为第一关键字从小到大排序,(pos)为第二关键字从大到小排序。如果序列合法,那么相邻两个(val)不相同的,前者的(pos)小于后者。

发现每个排列对应着一个合法的序列,构造方式:在pos前者小于后者的位置断开,每段表示某个(val)的分布。

现在考虑计算(i)的答案。枚举(j)表示对于第(j)位,排列([1,j])分成了(i)段(即有(j-i)处下降)。于是答案为(sum_{j=i}^nE(j,j-i)inom{n}{j}(n-j)!)。其中(E)为欧拉数。

为了好看一些改写成(sum_{j=i}^nE(j,i-1)inom{n}{j}(n-j)!),然后给(i)下标平移一位((iin[0,n-1])),于是(ans_i=sum_{j=i+1}^nE(j,i)inom{n}{j}(n-j)!)。为了更好看一些(j)的枚举下界改为(i),最后特殊减去(ans_0)多余的贡献即可。

然后就是喜闻乐见的推式子环节:

首先将欧拉数用第二类斯特林数表示。第二类斯特林数有生成函数表示:(S(n,k)=frac{1}{k!}(e^x-1)^k[x^n])

[ans_i=sum_{j=i}^n E(j,i)inom{n}{j}(n-j)!\ =sum_{j=i}^ninom{n}{j}(n-j)!sum_{k=i}^jinom{k}{i}(-1)^{k-i}(e^x-1)^{j-k}j![x^j]\ =n!sum_{k=i}^ninom{k}{i}(-1)^{k-i}sum_{j=k}^n(e^x-1)^{j-k}[x^j]\ =n!sum_{k=i}^ninom{k}{i}(-1)^{k-i}sum_{j=0}^{n-k}(e^x-1)^{j}[x^{j+k}]\ =n!sum_{k=i}^ninom{k}{i}(-1)^{k-i}sum_{j=0}^{n-k}(frac{e^x-1}{x})^{j}[x^{k}]\ ]

对于每个(kin[0,n])求出右边的东西,然后就可以卷积搞定。

[令F(x)=frac{e^x-1}{x},求出g_k=sum_{i=0}^{n-k}F^i[x^k]\ sum_{i=0}^{n-k}F^i=frac{1}{1-F}-frac{F^{n-k+1}}{1-F}\ frac{1}{1-F}很好算。计算frac{F^{n-k+1}}{1-F}[x^k]\ frac{F^{n-k+1}}{1-F}[x^k]\ =frac{(xF)^{n-k+1}}{1-F}[x^{n+1}]\ =[x^{n+1}y^{n-k+1}]sum_ifrac{(xyF)^{i}}{1-F}\ =[x^{n+1}y^{n-k+1}]frac{1}{1-xyF}frac{1}{1-F} ]

转化成多项式复合的形式(感觉这一步是推导的精髓?):

[设W(x)=xF(x),构造F(x)=H(W(x)),可得frac{W(x)}{H(W(x))}=x\ 设G(x)=frac{1}{1-xy}frac{1}{1-H(x)},则G(W(x))=frac{1}{1-xyF}frac{1}{1-F}\ 现在要求[x^{n+1}]G(W(x)) ]

拉格朗日反演。设(P(x))(W(x))的复合逆。带入(H)的定义式得(frac{x}{P(x)}=H(x))

[[x^{n+1}]G(W(x))\ =frac{1}{n+1}[x^n]G'(x)(frac{x}{P(x)})^{n+1}\ =frac{1}{n+1}[x^n]G'(x)H(x)^{n+1}\ =frac{1}{n+1}[x^n]left(frac{y}{(1-xy)^2(1-H(x))}+frac{H'(x)}{(1-xy)(1-H(x))^2} ight)H(x)^{n+1}\ 提取y^{k}项系数(kin[1,n+1]),并且忽略前面的常数:\ =[x^ny^k]left(frac{y}{(1-H(x))}sum_{ige 0}(i+1)(xy)^i+frac{H'(x)}{(1-H(x))^2}sum_{ige 0}(xy)^i ight)H(x)^{n+1}\ =[x^n]left(frac{kx^{k-1}}{1-H(x)}+frac{H'(x)x^k}{(1-H(x))^2} ight)H(x)^{n+1}\ =[x^{n-k+1}]frac{kH(x)^{n+1}}{1-H(x)}+[x^{n-k}]frac{H'(x)H(x)^{n+1}}{(1-H(x))^2}\ =[x^{n-k+2}]frac{kH(x)^{n+1}}{frac{1-H(x)}{x}}+[x^{n-k+2}]frac{H'(x)H(x)^{n+1}}{(frac{1-H(x)}{x})^2}\ ]

最后问题是求(H(x))

[frac{xF(x)}{H(xF(x))}=frac{e^x-1}{H(e^x-1)}=x\ 构造T(e^x-1)=x,可得T(x)=ln(1+x)\ 令z=e^x-1,得frac{z}{H(z)}=T(z)\ 把z换成x代入,H(x)=frac{x}{ln(1+x)} ]


using namespace std;
#include <bits/stdc++.h>
#define N (262144+10)
#define ll long long
#define mo 998244353
ll qpow(ll x,ll y=mo-2){
	ll r=1;
	for (;y;y>>=1,x=x*x%mo)
		if (y&1)
			r=r*x%mo;
	return r;
}
int n;
int g[N],ans[N];
ll fac[N],ifac[N],inv[N];
void initC(int n){
	fac[0]=1;
	for (int i=1;i<=n;++i)
		fac[i]=fac[i-1]*i%mo;
	ifac[n]=qpow(fac[n]);
	for (int i=n-1;i>=0;--i)
		ifac[i]=ifac[i+1]*(i+1)%mo;
	for (int i=1;i<=n;++i)
		inv[i]=ifac[i]*fac[i-1]%mo;
}
ll C(int m,int n){return fac[m]*ifac[n]%mo*ifac[m-n]%mo;}
int re[N],nN;
void setlen(int n){
	int bit=0;
	for (nN=1;nN<=n;nN<<=1,++bit);
	for (int i=1;i<nN;++i)
		re[i]=re[i>>1]>>1|(i&1)<<bit-1;
}
void dft(int A[],int flag){
	for (int i=0;i<nN;++i)
		if (i<re[i])
			swap(A[i],A[re[i]]);
	static int wnk[N];
	for (int i=1;i<nN;i<<=1){
		ll wn=qpow(3,flag==1?(mo-1)/(2*i):mo-1-(mo-1)/(2*i));
		wnk[0]=1;
		for (int k=1;k<i;++k)
			wnk[k]=wnk[k-1]*wn%mo;
		for (int j=0;j<nN;j+=i<<1)
			for (int k=0;k<i;++k){
				ll x=A[j+k],y=(ll)A[j+k+i]*wnk[k];
				A[j+k]=(x+y)%mo;
				A[j+k+i]=(x-y)%mo;
			}
	}
	for (int i=0;i<nN;++i)
		A[i]=(A[i]+mo)%mo;
	if (flag==-1){
		ll invn=qpow(nN);
		for (int i=0;i<nN;++i)
			A[i]=A[i]*invn%mo;
	}
}
void clear(int A[],int siz=nN){memset(A,0,sizeof(int)*siz);}
void multi(int c[],int a[],int b[],int n){
	static int A[N],B[N];
	setlen(n*2);
	clear(A),memcpy(A,a,sizeof(int)*(n+1)),dft(A,1);
	if (a==b)
		for (int i=0;i<nN;++i) A[i]=(ll)A[i]*A[i]%mo;
	else{
		clear(B),memcpy(B,b,sizeof(int)*(n+1)),dft(B,1);
		for (int i=0;i<nN;++i) A[i]=(ll)A[i]*B[i]%mo;
	}
	dft(A,-1);
	for (int i=0;i<=n*2;++i) c[i]=A[i];
}
void getinv(int c[],int a[],int n){
	static int b[N],A[N],B[N];
	int nn=1;
	for (;nn<n;nn<<=1);
	clear(b,nn);
//	assert(a[0]);
	b[0]=qpow(a[0]);
	for (int i=1;i<n;i<<=1){
		setlen(i*3-1);
		clear(A),clear(B);
		memcpy(A,a,sizeof(int)*min(n,i*2));
		memcpy(B,b,sizeof(int)*i);
		dft(A,1),dft(B,1);
		for (int j=0;j<nN;++j) B[j]=(ll)B[j]*B[j]%mo*A[j]%mo;
		dft(B,-1);
		for (int j=0;j<i*2;++j) b[j]=(2ll*b[j]-B[j]+mo)%mo;
	}
	memcpy(c,b,sizeof(int)*n);
}
void getln(int c[],int a[],int n){
	static int b[N],d[N];
	for (int i=1;i<n;++i) b[i-1]=(ll)a[i]*i%mo;
	getinv(d,a,n);
	multi(b,b,d,n-1);
	c[0]=0;
	for (int i=0;i<n-1;++i)
		c[i+1]=b[i]*inv[i+1]%mo;
}
void getexp(int c[],int a[],int n){
	static int b[N],d[N];
	int nn=1;
	for (;nn<n;nn<<=1);
	clear(b,nn);
	b[0]=1;
	for (int i=1;i<n;i<<=1){
		getln(d,b,i*2);
		for (int j=0;j<i*2;++j)
			d[j]=(a[j]-d[j]+mo)%mo;
		d[0]=(d[0]+1)%mo;
		multi(d,b,d,i*2-1);
		memcpy(b,d,sizeof(int)*(i*2));
	}
	memcpy(c,b,sizeof(int)*n);
}
void getpow(int c[],int a[],int n,int idx){
	static int b[N];
//	assert(a[0]);
	getln(b,a,n);
	for (int i=0;i<n;++i)
		b[i]=(ll)b[i]*idx%mo;
	getexp(c,b,n);
}
void work0(){
	static int a[N];
	for (int i=2;i<=n+3;++i)
		a[i-2]=(mo-ifac[i])%mo;
	getinv(a,a,n+2);
	for (int k=0;k<=n;++k)
		g[k]=(g[k]+a[k+1])%mo;
}
void work1(){
	static int H[N],P[N],a[N],b[N];
	for (int i=1;i<=n+3;++i)
		H[i-1]=(-(i&1?-1:1)*inv[i]+mo)%mo;
	getinv(H,H,n+3);
	getpow(P,H,n+2,n+1);
	
	for (int i=1;i<=n+2;++i)
		a[i-1]=(mo-H[i])%mo;
	getinv(a,a,n+2);
	multi(b,P,a,n+2-1);
	for (int k=0;k<=n;++k){
		int k_=n-k+1;
		g[k]=((g[k]-(ll)k_*b[n-k_+2]%mo*inv[n+1])%mo+mo)%mo;
	}
	
	multi(a,a,a,n+2-1);
	for (int i=1;i<=n+2;++i)
		b[i-1]=(ll)H[i]*i%mo;
	multi(b,b,P,n+2-1);
	multi(b,b,a,n+2-1);
	for (int k=0;k<=n;++k){
		int k_=n-k+1;
		g[k]=((g[k]-(ll)b[n-k_+2]*inv[n+1])%mo+mo)%mo;
	}
}
void work2(){
	static int a[N],b[N],c[N];
	for (int k=0;k<=n;++k) a[k]=fac[k]*g[k]%mo;
	for (int k=0;k<=n;++k) b[n-k]=((k&1?-1:1)*ifac[k]+mo)%mo;
	multi(c,a,b,n);
	for (int i=0;i<n;++i)
		ans[i]=c[n+i]*fac[n]%mo*ifac[i]%mo;
}
int main(){
	scanf("%d",&n);
	initC(n+5);
	work0();
	work1();
	work2();
	ans[0]=(ans[0]-fac[n]+mo)%mo;
	for (int i=0;i<n;++i)
		printf("%d ",ans[i]);
	return 0;
}
原文地址:https://www.cnblogs.com/jz-597/p/14708492.html