反演复习计划51nod1594Gcd and Phi

Posted 2020-09-19 zcysky

现在感觉反演好多都是套路QAQ……

#include<bits/stdc++.h>
using namespace std;
const int N=2e6+5;
typedef long long ll;
int n,cnt,prime[N],phi[N],mu[N],vis[N];
ll ans,s[N],f[N];
void calcmu(){
    memset(prime,0,sizeof(prime));cnt=0;
    memset(phi,0,sizeof(phi));memset(mu,0,sizeof(mu));
    memset(s,0,sizeof(s));memset(f,0,sizeof(f));
    mu[1]=1;phi[1]=1;memset(vis,1,sizeof(vis));
    for(int i=2;i<=n;i++){
        if(vis[i]){prime[++cnt]=i;mu[i]=-1;phi[i]=i-1;}
        for(int j=1;j<=cnt;j++){
            int t=prime[j]*i;if(t>n)break;
            vis[t]=0;
            if(i%prime[j]==0){
                mu[t]=0;phi[t]=phi[i]*prime[j];
                break;
            }
            mu[t]=-mu[i];phi[t]=phi[i]*(prime[j]-1);
        }
    }
    for(int i=1;i<=n;i++)s[phi[i]]++;
    for(int i=1;i<=n;i++)
    for(int j=i;j<=n;j+=i)f[i]+=s[j];
    for(int i=1;i<=n;i++)f[i]=f[i]*f[i];
    for(int i=1;i<=n;i++)if(mu[i]!=0)
    for(int d=1;i*d<=n;d++)ans+=mu[i]*phi[d]*f[i*d];
    printf("%lld\n",ans);
}
inline int read(){
    int f=1,x=0;char ch;
    do{ch=getchar();if(ch==‘-‘)f=-1;}while(ch<‘0‘||ch>‘9‘);
    do{x=x*10+ch-‘0‘;ch=getchar();}while(ch>=‘0‘&&ch<=‘9‘);
    return f*x;
}
int main(){
    int T=read();
    while(T--){
        n=read();ans=0;calcmu();
    }
}

现在没有爱蜜莉雅碳陪我做题啦TAT