Bzoj-2820 YY的GCD Mobius反演,分块

时间:2023-03-09 00:38:24
Bzoj-2820 YY的GCD Mobius反演,分块

  题目链接:http://www.lydsy.com/JudgeOnline/problem.php?id=2820

  题意:多次询问,求1<=x<=N, 1<=y<=M且gcd(x,y)为质数有多少对。

  首先,   Bzoj-2820 YY的GCD Mobius反演,分块

  由于这里是多次询问,并且数据很大,显然不能直接求解,需要做如下处理。。

  整数的除法是满足结合律的,然后我们设T=p*d,有:Bzoj-2820 YY的GCD Mobius反演,分块

  注意到后面部分是可以预处理出来的,那么整个ans就可以用分块处理来求了,设Bzoj-2820 YY的GCD Mobius反演,分块

  那么有Bzoj-2820 YY的GCD Mobius反演,分块,考虑当p|x时,根据莫比菲斯mu(x)的性质,px除以其它非p的质数因数都为0,所以g(px)=mu(x)。当p!|x时,除数为p时为mu(x),否则其它的和为-g(x),因为这里还乘了一个p所以要变反。然后O(n)预处理下就可以了。。

 //STATUS:C++_AC_3660MS_274708KB
#include <functional>
#include <algorithm>
#include <iostream>
//#include <ext/rope>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cstring>
#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bitset>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <list>
#include <set>
//#include <map>
using namespace std;
//#pragma comment(linker,"/STACK:102400000,102400000")
//using namespace __gnu_cxx;
//define
#define pii pair<int,int>
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define PI acos(-1.0)
//typedef
typedef long long LL;
typedef unsigned long long ULL;
//const
const int N=;
const int INF=0x3f3f3f3f;
const int MOD=,STA=;
const LL LNF=1LL<<;
const double EPS=1e-;
const double OO=1e15;
const int dx[]={-,,,};
const int dy[]={,,,-};
const int day[]={,,,,,,,,,,,,};
//Daily Use ...
inline int sign(double x){return (x>EPS)-(x<-EPS);}
template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
template<class T> inline T Min(T a,T b){return a<b?a:b;}
template<class T> inline T Max(T a,T b){return a>b?a:b;}
template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
//End LL sum[N],g[N];
int isprime[N],mu[N],prime[N];
int cnt;
int T,n,m; void Mobius(int n)
{
int i,j;
//Init isprime[N],mu[N],prime[N],全局变量初始为0
cnt=;mu[]=;
for(i=;i<=n;i++){
if(!isprime[i]){
prime[cnt++]=i;
mu[i]=-;
g[i]=;
}
for(j=;j<cnt && i*prime[j]<=n;j++){
isprime[i*prime[j]]=;
if(i%prime[j]){
mu[i*prime[j]]=-mu[i];
g[i*prime[j]]=mu[i]-g[i];
}
else {
mu[i*prime[j]]=;
g[i*prime[j]]=mu[i];
break;
}
}
}
for(i=;i<=n;i++)sum[i]=sum[i-]+g[i];
} int main(){
// freopen("in.txt","r",stdin);
int i,j,la;
LL ans;
Mobius();
scanf("%d",&T);
while(T--)
{
scanf("%d%d",&n,&m); if(n>m)swap(n,m);
ans=;
for(i=;i<=n;i=la+){
la=Min(n/(n/i),m/(m/i));
ans+=(sum[la]-sum[i-])*(n/i)*(m/i);
} printf("%lld\n",ans);
}
return ;
}