【欧拉函数表】POJ2478-Farey Sequence

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
const int MAXN=1000000+50;
typedef long long ll;
int n,maxn;
int phi[MAXN],p[MAXN],input[MAXN];
ll s[MAXN];
int t=0;

void eular_table()
{
memset(phi,0,sizeof(phi));
memset(p,0,sizeof(p));
p[0]=1;p[1]=2;phi[2]=1;
for (int i=2;i<=maxn;i++)
{
if (phi[i]==0)
{
p[++p[0]]=i;
phi[i]=i-1;
}
for (int j=1;j<=p[0];j++)
{
if (i*p[j]<=maxn) phi[i*p[j]]=(i%p[j]==0)? phi[i]*p[j] : phi[i]*(p[j]-1);
//注意一定要保证i*p[j]没有超出数组上界，否则RE
else break;
}
}
}

void printans()
{
s[0]=0;
for (int i=1;i<=maxn;i++)
s[i]=s[i-1]+phi[i];
for (int i=0;i<t;i++)
printf("%lld\n",s[input[i]]);
}

int main()
{
while (~scanf("%d",&n) && n!=0)
{
input[t++]=n;
maxn=max(maxn,n);
}
eular_table();
printans();
return 0;
}