洛谷 P3704 [SDOI2017]数字表格(莫比乌斯函数)

题面传送门

题意:

[prodlimits_{i=1}^nprodlimits_{j=1}^mfib_{gcd(i,j)} ]

(T) 组测试数据,(1 leq T leq 10^3)(1 leq n,m leq 10^6)

没啥好说的,直接推式子。

[egin{aligned}ans&=prodlimits_{i=1}^nprodlimits_{j=1}^mfib_{gcd(i,j)}\&=prodlimits_{d=1}^{min(n,m)}prodlimits_{i=1}^nprodlimits_{j=1}^mfib_d imes[gcd(i,j)=d]\&=prodlimits_{d=1}^{min(n,m)}fib_d^{sumlimits_{i=1}^{lfloorfrac{n}{d} floor}sumlimits_{j=1}^{lfloorfrac{m}{d} floor}[gcd(i,j)=1]}end{aligned} ]

设指数上的那一大堆玩意儿为 (M),那么

[egin{aligned}M&=sumlimits_{i=1}^{lfloorfrac{n}{d} floor}sumlimits_{j=1}^{lfloorfrac{m}{d} floor}[gcd(i,j)=1]\&=sumlimits_{i=1}^{lfloorfrac{n}{d} floor}sumlimits_{j=1}^{lfloorfrac{m}{d} floor}sumlimits_{p|gcd(i,j)}mu(p)\&=sumlimits_{p=1}^{lfloorfrac{min(n,m)}{d} floor}mu(p) imeslfloorfrac{n}{dp} floorlfloorfrac{m}{dp} floorend{aligned} ]

[egin{aligned}ans&=prodlimits_{d=1}^{min(n,m)}fib_d^M\&=prodlimits_{d=1}^{min(n,m)}fib_d^{sumlimits_{p=1}^{lfloorfrac{min(n,m)}{d} floor}mu(p) imeslfloorfrac{n}{dp} floorlfloorfrac{m}{dp} floor}\&=prodlimits_{t=1}^{min(n,m)}prodlimits_{d|t}fib_d^{mu(frac{t}{d}) imeslfloorfrac{n}{t} floorlfloorfrac{m}{t} floor}\&=prodlimits_{t=1}^{min(n,m)}(prodlimits_{d|t}fib_d^{mu(frac{t}{d})})^{lfloorfrac{n}{t} floorlfloorfrac{m}{t} floor}end{aligned} ]

把括号里的东西预处理出来然后整除分块就行了

/*
Contest: -
Problem: P3704
Author: tzc_wk
Time: 2020.9.16
*/
#include <bits/stdc++.h>
using namespace std;
#define fi			first
#define se			second
#define pb			push_back
#define fz(i,a,b)	for(int i=a;i<=b;i++)
#define fd(i,a,b)	for(int i=a;i>=b;i--)
#define foreach(it,v) for(__typeof(v.begin()) it=v.begin();it!=v.end();it++)
#define all(a)		a.begin(),a.end()
#define fill0(a)	memset(a,0,sizeof(a))
#define fill1(a)	memset(a,-1,sizeof(a))
#define fillbig(a)	memset(a,0x3f,sizeof(a))
#define y1			y1010101010101
#define y0			y0101010101010
#define int long long
typedef pair<int,int> pii;
typedef long long ll;
inline int read(){
	int x=0,neg=1;char c=getchar();
	while(!isdigit(c)){
		if(c=='-') neg=-1;
		c=getchar();
	}
	while(isdigit(c)) x=x*10+c-'0',c=getchar();
	return x*neg;
}
const int MOD=1e9+7;
inline int qpow(int x,int e){
	if(!x) return 1;
	int ans=1;
	while(e){
		if(e&1) ans=ans*x%MOD;
		x=x*x%MOD;e>>=1;
	}
	return ans;
}
int f[1000005],mu[1000005],p[1000005],pcnt=0,F[1000005];
bool vis[1000005];
inline void prework(int n){
	f[1]=f[2]=1;
	for(int i=3;i<=n;i++)
		f[i]=(f[i-1]+f[i-2])%MOD;
	mu[1]=1;
	for(int i=2;i<=n;i++){
		if(!vis[i]){p[++pcnt]=i;mu[i]=-1;}
		for(int j=1;j<=pcnt&&p[j]*i<=n;j++){
			vis[i*p[j]]=1;
			if(i%p[j]==0) break;
			mu[i*p[j]]=-mu[i];
		}
	}
	for(int i=1;i<=n;i++) F[i]=1;
	for(int i=1;i<=n;i++){
		int inv=qpow(f[i],MOD-2);
		for(int j=i;j<=n;j+=i){
			if(!mu[j/i]) continue;
			else if(~mu[j/i]) F[j]=F[j]*f[i]%MOD;
			else F[j]=F[j]*inv%MOD;
		}
	}
	for(int i=2;i<=n;i++)
		F[i]=F[i-1]*F[i]%MOD;
}
signed main(){
	prework(1e6);
	int T=read();
	while(T--){
		int n=read(),m=read(),ans=1;
		for(int l=1,r;l<=min(n,m);l=r+1){
			r=min(n/(n/l),m/(m/l));
			ans=(ans*(qpow(F[r]*qpow(F[l-1],MOD-2)%MOD,(n/l)*(m/l)%(MOD-1))))%MOD;
		}
		printf("%lld
",ans);
	}
	return 0;
}
原文地址:https://www.cnblogs.com/ET2006/p/luogu-P3704.html