洛谷 P5518

洛谷题面传送门

一道究极恶心的毒瘤六合一题,式子推了我满满两面 A4 纸……

首先我们可以将式子拆成:

[ans=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^C(dfrac{ij}{gcd(i,j)gcd(i,j)})^{f(type)} ]

也就是说我们需要算出以下四项式子的值:

[prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^Ci^{f(type)} ]

[prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^Cj^{f(type)} ]

[prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^C(dfrac{1}{gcd(i,j)})^{f(type)} ]

[prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^C(dfrac{1}{gcd(i,k)})^{f(type)} ]

显然前两项与后两项是等价的,因此我们只需算出:

[f_1(type)=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^Ci^{f(type)} ]

[f_2(type)=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^C(gcd(i,j))^{f(type)} ]

即可求出答案。


考虑对 (type) 进行分类讨论,首先是 (type=0),那么

[f_1(0)=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^Ci ]

考虑每个 (i) 的贡献,稍微想想即可得到:

[f_1(0)=(A!)^{BC} ]

然后是 (f_2(0)),套路地枚举 (gcd(i,j))

[egin{aligned} f_2(0)&=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^Cgcd(i,j)\ &=(prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{i=1}^Asumlimits_{j=1}^B[gcd(i,j)=d]})^C\ &=(prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{i=1}^{A/d}sumlimits_{j=1}^{B/d}[gcd(i,j)=1]})^C\ &=(prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{p}mu(p)lfloorfrac{A}{dp} floorlfloorfrac{B}{dp} floor})^C\ end{aligned} ]

最右边那个 (k) 次方显然可以忽略掉不管它,最后求个快速幂即可。考虑对里面的 (dp) 进行二维的整除分块,那么答案的式子可以化为:

[egin{aligned} f_2(0)=(prodlimits_{dp}g_1(dp)^{lfloorfrac{A}{dp} floorlfloorfrac{B}{dp} floor})^C end{aligned} ]

其中

[g_1(x)=prodlimits_{d·p=x}d^{mu(p)} ]

考虑整除分块,对于一段区间 ([L,R]),满足 (forall xin[L,R]) 均有 (lfloordfrac{A}{x} floor=lfloordfrac{A}{L} floor,lfloordfrac{B}{x} floor=lfloordfrac{B}{L} floor),我们这样计算它们的贡献:

[prodlimits_{i=L}^R(g_1(i)^{lfloorfrac{A}{i} floorlfloorfrac{B}{i} floor})^C=(prodlimits_{i=L}^Rg_1(i))^{lfloorfrac{A}{i} floorlfloorfrac{B}{i} floor·C} ]

预处理前缀积即可 (mathcal O(1)) 计算,时间复杂度 (mathcal O(log nsqrt{n}))


接下来是 (type=1) 的情况,个人感觉与 (type=0) 的情况大差不差,毕竟指数上都只与 (i,j,k) 本身而不涉及到它们的 (gcd) 之类,只不过指数上枚举变量的次数稍微高了一点点,导致情况较于 (type=0) 略有一点点繁琐。

首先是 (f_1(1))

[f_1(1)=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^Ci^{ijk} ]

还是考虑每个 (i) 的贡献被累计了多少次:

[egin{aligned} f_1(0)&=(A!)^{sumlimits_{j=1}^Bsumlimits_{k=1}^Cjk}\ &=(A!)^{frac{B(B+1)}{2}·frac{C(C+1)}{2}} end{aligned} ]

一波快速幂带走。

其次是 (f_2(1))

[egin{aligned} f_2(1)&=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^Cgcd(i,j)^{ijk}\ &=(prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{i=1}^Asumlimits_{j=1}^Bij[gcd(i,j)=d]})^{sumlimits_{k=1}^Ck}\ &=(prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{i=1}^{A/d}sumlimits_{j=1}^{B/d}ijd^2[gcd(i,j)=1]})^{frac{C(C+1)}{2}}\ &=(prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{p}mu(p)d^2p^2·s(lfloorfrac{A}{dp} floor)s(lfloorfrac{B}{dp} floor)})^{frac{C(C+1)}{2}}\ end{aligned} ]

其中 (s(i)=dfrac{i(i+1)}{2})

那么我们还是枚举 (dp),按照 (f_2(0)) 的套路设一个 (g_2(x)),定义如下:

[g_2(x)=prodlimits_{d·p=x}d^{d^2p^2mu(p)} ]

那么考虑对 (dp) 进行整除分块,那么

[f_2(1)=(prodlimits_{dp=1}^{min(A,B)}g_2(dp)^{s(lfloorfrac{A}{dp} floor)s(lfloorfrac{B}{dp} floor)})^{frac{C(C+1)}{2}} ]

预处理 (g_2(dp)) 的前缀积然后对 (dp) 整除分块即可。


最后是 (type=2) 的情况

先考虑 (f_1(2))

[f_1(2)=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^Ci^{gcd(i,j,k)} ]

上来先把 (gcd) 反演掉:

[egin{aligned} f_1(2)&=prodlimits_{d=1}^{min(A,B,C)}prodlimits_{i=1}^{lfloorfrac{A}{d} floor}(id)^{d·sumlimits_{j=1}^{lfloorfrac{B}{d} floor}sumlimits_{k=1}^{lfloorfrac{C}{d} floor}[gcd(i,j,k)=1]}\ &=prodlimits_{d=1}^{min(A,B,C)}prodlimits_{i=1}^{lfloorfrac{A}{d} floor}(id)^{d·sumlimits_{pmid i}mu(p)lfloorfrac{B}{dp} floorlfloorfrac{C}{dp} floor} end{aligned} ]

(p) 提到外面来

[egin{aligned} f_1(2)&=prodlimits_{d=1}^{min(A,B,C)}prodlimits_{p}(prodlimits_{iin[1,lfloorfrac{A}{d} floor]&pmid i}(id)^{d·mu(p)})^{lfloorfrac{B}{dp} floorlfloorfrac{C}{dp} floor} end{aligned} ]

然后按照套路枚举 (dfrac{i}{p})

[egin{aligned} f_1(2)&=prodlimits_{d=1}^{min(A,B,C)}prodlimits_{p}(prodlimits_{i=1}^{lfloorfrac{A}{dp} floor}(idp)^{d·mu(p)})^{lfloorfrac{B}{dp} floorlfloorfrac{C}{dp} floor} end{aligned} ]

然后枚举 (dp),根据 (mu*i=varphi) 可知 (sumlimits_{d·p=x}d·mu(p)=varphi(x)),于是

[f_1(2)=prodlimits_{x=1}^{min(A,B,C)}(prodlimits_{i=1}^{lfloorfrac{A}{x} floor}(ix)^{varphi(x)})^{lfloorfrac{B}{x} floorlfloorfrac{C}{x} floor} ]

外面的东西显然整除分块一下就好了,里面的东西

[prodlimits_{i=1}^{lfloorfrac{A}{x} floor}(ix)^{varphi(x)} ]

显然等于

[egin{aligned} &prodlimits_{i=1}^{lfloorfrac{A}{x} floor}i^{varphi(x)}·x^{varphi(x)}\ =&((lfloordfrac{A}{x} floor)!)^{varphi(x)}·(x^{varphi(x)})^{lfloorfrac{A}{x} floor} end{aligned} ]

然后套路地预处理 (g_3=x^{varphi(x)}) 的前缀积,以及 (varphi(x)) 的前缀和即可在整除分块的过程中 (mathcal O(1)) 求出式子的值,注意 (varphi(x)) 的前缀和应 (mod(MOD-1)) 而不是 (mod MOD),因为 (varphi(x)) 的前缀和作用在指数上。

时间复杂度 (sqrt{n}log n)

然后是最精神污染的一个式子:

[f_2(2)=prodlimits_{i=1}^Aprodlimits_{j=1}^Bprodlimits_{k=1}^C(gcd(i,j))^{gcd(i,j,k)} ]

按照 P1587 的套路,碰到两个 (gcd) 咱们最好不要莽,要一个个反演,因此考虑先反演下面这个 (gcd)

[egin{aligned} f_2(2)&=prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{i=1}^{lfloorfrac{A}{d} floor}sumlimits_{j=1}^{lfloorfrac{B}{d} floor}[gcd(i,j)=1]sumlimits_{k=1}^Cgcd(d,k)}\ &=prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{p}^{lfloorfrac{min(A,B)}{d} floor}mu(p)lfloorfrac{A}{dp} floorlfloorfrac{B}{dp} floorsumlimits_{k=1}^Cgcd(d,k)} end{aligned} ]

发现后面有个 (sumlimits_{k=1}^Cgcd(d,k)),考虑对这个东西单独推个式子:

[egin{aligned} g_4(d,C)&=sumlimits_{k=1}^Cgcd(d,k)\ &=sumlimits_{xmid d}x·sumlimits_{i=1}^{lfloorfrac{C}{x} floor}[iperpdfrac{d}{x}]\ &=sumlimits_{xmid d}x·sumlimits_{ymidfrac{d}{x}}mu(y)lfloordfrac{C}{xy} floor end{aligned} ]

套路地枚举 (xy=T) 可得:

[g_4(d,C)=sumlimits_{Tmid d}lfloordfrac{C}{T} floorsumlimits_{xmid T}xmu(dfrac{T}{x}) ]

这已经是本题中第二次看到这个式子了:

[sumlimits_{xmid T}xmu(dfrac{T}{x})=varphi(T) ]

于是

[g_4(d,C)=sumlimits_{Tmid d}lfloordfrac{C}{T} floorvarphi(T) ]

带回去

[f_2(2)=prodlimits_{d=1}^{min(A,B)}d^{sumlimits_{p}^{lfloorfrac{min(A,B)}{d} floor}mu(p)lfloorfrac{A}{dp} floorlfloorfrac{B}{dp} floorsumlimits_{Tmid d}lfloorfrac{C}{T} floorvarphi(T)} ]

按照这里总结出来的套路,看到先枚举 (i) 再枚举 (jmid i) 的求和/积式我们可以考虑交换求和/积的顺序,先枚举 (j) 再枚举 (i),这样会出现下取整,就可以整除分块了。

因此考虑先枚举 (T) 再枚举 (d),有:

[f_2(2)=prodlimits_{T=1}^{min(A,B)}prodlimits_{d=1}^{lfloorfrac{min(A,B)}{T} floor}(dT)^{sumlimits_{p}mu(p)lfloorfrac{A}{dTp} floorlfloorfrac{B}{dTp} floorlfloorfrac{C}{T} floorvarphi(T)} ]

然后考虑拆开来:

[f_2(2)=prodlimits_{T=1}^{min(A,B)}(T^{varphi(T)lfloorfrac{C}{T} floor})^{sumlimits_{d}sumlimits_{p}mu(p)lfloorfrac{A}{dTp} floorlfloorfrac{B}{dTp} floor}·prodlimits_{d=1}^{lfloorfrac{min(A,B)}{T} floor}(d^{sumlimits_{p}mu(p)lfloorfrac{A}{dTp} floorlfloorfrac{B}{dTp} floor})^{varphi(T)lfloorfrac{C}{T} floor} ]


先考虑前面的式子:

[(T^{varphi(T)lfloorfrac{C}{T} floor})^{sumlimits_{d}sumlimits_{p}mu(p)lfloorfrac{A}{dTp} floorlfloorfrac{B}{dTp} floor} ]

考虑枚举 (dp=x),那么:

[egin{aligned} ext{原式}&=(T^{varphi(T)lfloorfrac{C}{T} floor})^{sumlimits_{x}sumlimits_{pmid x}mu(p)lfloorfrac{A}{Tx} floorlfloorfrac{B}{Tx} floor}\ &=(T^{varphi(T)lfloorfrac{C}{T} floor})^{epsilon(x)lfloorfrac{A}{Tx} floorlfloorfrac{B}{Tx} floor}\ &=(T^{varphi(T)lfloorfrac{C}{T} floor})^{lfloorfrac{A}{T} floorlfloorfrac{B}{T} floor} end{aligned} ]

(T) 整除分块一下,预处理 (varphi(T)) 的前缀和即可 (mathcal O(1)) 算出。


然后是后面的式子(胜利就在眼前!)

[prodlimits_{T=1}^{min(A,B)}prodlimits_{d=1}^{lfloorfrac{min(A,B)}{T} floor}(d^{sumlimits_{p}mu(p)lfloorfrac{A}{dTp} floorlfloorfrac{B}{dTp} floor})^{varphi(T)lfloorfrac{C}{T} floor} ]

还是对 (T) 整除分块,然后枚举 (dp=x),那么上面的式子可以写成:

[prodlimits_{T=1}^{min(A,B)}prodlimits_{x=1}^{lfloorfrac{min(A,B)}{T} floor}((prodlimits_{dmid x}d^{mu(p)})^{lfloorfrac{A}{Tx} floorlfloorfrac{B}{Tx} floor})^{varphi(T)lfloorfrac{C}{T} floor} ]

发现最里面的括号的东西就是在求 (f_2(0)) 时用到的 (g_1(x)),那么我们再套一个对 (x) 的整除分块即可。

根据整除分块里再套一个整除分块复杂度是 (sumlimits_{x,exists k,s.t.lfloorfrac{n}{k} floor=x}sqrt{x}=n^{0.75}) 可知这一部分复杂度为 (n^{0.75}log n)

于是这题就做完了,时间复杂度 (nlog n+Tn^{0.75}log n)


关于此题的常数问题,由于取模运算较多,可以使用快速取模优化常数,具体可见 chenxia25 神仙的这篇博客

const int MAXV=1e5;
ll mod;
int pr[MAXV/5+5],prcnt=0,vis[MAXV+5],mu[MAXV+5],smu[MAXV+5],phi[MAXV+5];
int fac[MAXV+5],prd[MAXV+5],prd_inv[MAXV+5],prd_sq[MAXV+5],prd_sq_inv[MAXV+5];
int pre_ii[MAXV+5],inv_pre_ii[MAXV+5],pre_mul[MAXV+5],inv_pre_mul[MAXV+5];
int inv[MAXV+5],prd_phi[MAXV+5],prd_phi_inv[MAXV+5];
int sphi[MAXV+5];
__int128_t _base1=1,_base2=1;
inline int mol1(__int128_t x){return x-mod*(_base1*x>>64);}
inline int mol2(__int128_t x){return x-(mod-1)*(_base2*x>>64);}
int qpow(int x,int e){
	if(e<0) e+=mod-1;int ret=1;
	for(;e;e>>=1,x=mol1(1ll*x*x)) if(e&1) ret=mol1(1ll*ret*x);
	return ret;
}
int work(int x,int y){return (!y)?1:((~y)?x:inv[x]);}
void sieve(int n){
	for(int i=(inv[0]=inv[1]=1)+1;i<=n;i++) inv[i]=mol1(1ll*inv[mod%i]*(mod-mod/i));
	mu[1]=phi[1]=1;
	for(int i=(fac[0]=1);i<=n;i++) fac[i]=mol1(1ll*fac[i-1]*i);
	for(int i=2;i<=n;i++){
		if(!vis[i]) mu[i]=-1,pr[++prcnt]=i,phi[i]=i-1;
		for(int j=1;j<=prcnt&&pr[j]*i<=n;j++){
			vis[pr[j]*i]=1;
			if(i%pr[j]==0){phi[i*pr[j]]=phi[i]*pr[j];break;}
			mu[i*pr[j]]=-mu[i];phi[i*pr[j]]=phi[i]*phi[pr[j]];
		}
	}
	for(int i=1;i<=n;i++) smu[i]=smu[i-1]+mu[i];
	for(int i=0;i<=n;i++) prd[i]=prd_sq[i]=1;
	for(int i=1;i<=n;i++) for(int j=i;j<=n;j+=i) prd[j]=mol1(1ll*prd[j]*work(i,mu[j/i]));
	for(int i=1;i<=n;i++) prd[i]=mol1(1ll*prd[i-1]*prd[i]);
	for(int i=0;i<=n;i++) prd_inv[i]=qpow(prd[i],-1);
	for(int i=1;i<=n;i++) for(int j=i;j<=n;j+=i)
		prd_sq[j]=mol1(1ll*prd_sq[j]*
		qpow(qpow(i,mol2(1ll*i*i)),mol2(1ll*mu[j/i]*(j/i)*(j/i))));
	for(int i=1;i<=n;i++) prd_sq[i]=mol1(1ll*prd_sq[i-1]*prd_sq[i]);
	for(int i=0;i<=n;i++) prd_sq_inv[i]=qpow(prd_sq[i],-1);
	pre_ii[0]=1;for(int i=1;i<=n;i++) pre_ii[i]=mol1(1ll*pre_ii[i-1]*qpow(i,i));
	for(int i=0;i<=n;i++) inv_pre_ii[i]=qpow(pre_ii[i],-1);
	pre_mul[0]=1;for(int i=1;i<=n;i++) pre_mul[i]=mol1(1ll*pre_mul[i-1]*work(i,mu[i]));
	for(int i=0;i<=n;i++) inv_pre_mul[i]=qpow(pre_mul[i],-1);
	prd_phi[0]=1;for(int i=1;i<=n;i++) prd_phi[i]=mol1(1ll*prd_phi[i-1]*qpow(i,phi[i]));
	for(int i=0;i<=n;i++) prd_phi_inv[i]=qpow(prd_phi[i],-1);
	for(int i=1;i<=n;i++) sphi[i]=mol2(sphi[i-1]+phi[i]);
}
int calc1(int x,int y){
	int res=1;
	for(int l=1,r;l<=min(x,y);l=r+1){
		r=min(x/(x/l),y/(y/l));
		res=1ll*res*qpow(1ll*prd[r]*prd_inv[l-1]%mod,1ll*(x/l)*(y/l)%(mod-1))%mod;
	}
	return res;
}
int solve1(int a,int b,int c){
	int res=1ll*qpow(calc1(a,b),-c)*qpow(calc1(a,c),-b)%mod;
	res=1ll*res*qpow(fac[a],1ll*b*c%(mod-1))%mod;
	res=1ll*res*qpow(fac[b],1ll*a*c%(mod-1))%mod;
	return res;
}
ll get(int x){return mol2(1ll*x*(x+1)/2);}
int calc2(int x,int y){
	int res=1;
	for(int l=1,r;l<=min(x,y);l=r+1){
		r=min(x/(x/l),y/(y/l));
		res=1ll*res*qpow(1ll*prd_sq[r]*prd_sq_inv[l-1]%mod,
		1ll*get(x/l)*get(y/l)%(mod-1))%mod;
	}
	return res;
}
int solve2(int a,int b,int c){
	int res=1;
	res=1ll*res*qpow(pre_ii[a],(1ll*b*(b+1)>>1)%(mod-1))%mod;
	res=1ll*res*qpow(pre_ii[b],(1ll*a*(a+1)>>1)%(mod-1))%mod;
	res=1ll*res*qpow(calc2(a,b),mod-2)%mod;
	res=qpow(res,(1ll*c*(c+1)>>1)%(mod-1));
	res=1ll*res*qpow(calc2(a,c),-(1ll*b*(b+1)>>1)%(mod-1))%mod;
	return res;
}
int calc3(int x,int y,int z){
	int res=1;
	for(int l=1,r;l<=x;l=r+1){
		r=1e9;
		if(x/l) chkmin(r,x/(x/l));
		if(y/l) chkmin(r,y/(y/l));
		if(z/l) chkmin(r,z/(z/l));
		int mul=qpow(1ll*prd_phi[r]*prd_phi_inv[l-1]%mod,x/l);
		mul=1ll*mul*qpow(fac[x/l],sphi[r]-sphi[l-1])%mod;
		res=1ll*res*qpow(mul,1ll*(y/l)*(z/l)%(mod-1))%mod;
	} return res;
}
int calc4(int x,int y,int z){
	int res=1;
	for(int l=1,r;l<=min(x,y);l=r+1){
		r=1e9;
		if(x/l) chkmin(r,x/(x/l));
		if(y/l) chkmin(r,y/(y/l));
		if(z/l) chkmin(r,z/(z/l));
		res=1ll*res*qpow(1ll*prd_phi[r]*prd_phi_inv[l-1]%mod,1ll*(x/l)*(y/l)*(z/l)%(mod-1))%mod;
		int X=x/l,Y=y/l,Z=z/l,sm=1ll*Z*(sphi[r]-sphi[l-1])%(mod-1);
		for(int L=1,R;L<=min(X,Y);L=R+1){
			R=1e9;
			if(X/L) chkmin(R,X/(X/L));
			if(Y/L) chkmin(R,Y/(Y/L));
			res=1ll*res*qpow(1ll*prd[R]*prd_inv[L-1]%mod,1ll*(X/L)*(Y/L)*sm%(mod-1))%mod;
		}
	}
	return res;
}
int solve3(int x,int y,int z){
	return 1ll*calc3(x,y,z)*calc3(y,x,z)%mod*
	qpow(calc4(x,y,z),-1)%mod*qpow(calc4(x,z,y),-1)%mod;
}
int main(){
	int qu;scanf("%d%lld",&qu,&mod);
	_base1=(_base1<<64)/mod;_base2=(_base2<<64)/(mod-1);
	sieve(MAXV);
	while(qu--){
		int a,b,c;scanf("%d%d%d",&a,&b,&c);
		printf("%d %d %d
",solve1(a,b,c),solve2(a,b,c),solve3(a,b,c));
	}
	return 0;
}
原文地址:https://www.cnblogs.com/ET2006/p/luogu-P5518.html