UVA 10539 Almost Prime Numbers

Almost prime numbers are the non-prime numbers which are divisible by only a single prime number.

In this problem your job is to write a program which finds out the number of almost prime numbers

within a certain range.

Input

First line of the input file contains an integer N (N ≤ 600) which indicates how many sets of inputs

are there. Each of the next N lines make a single set of input. Each set contains two integer numbers

low and high (0 < low ≤ high < 1012).

Output

For each line of input except the first line you should produce one line of output. This line contains

a single integer, which indicates how many almost prime numbers are within the range (inclusive)

low … high.

Sample Input

3

1 10

1 20

1 5

Sample Output

3

4

1

求[l,r]中有多少个数满足它本身不是质数，但只有一个质因子。

先打出1-1e6的质数表。

每一个质数x，他最大贡献就是x^p<=n，就是log(x,n)。

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
const int N=1000005;
int n,cnt,pri
;
bool vis
;
long long query(long long pos)
{
long long ans=0;
for(int i=1;i<=cnt&&(long long)pri[i]*pri[i]<=pos;i++)
ans+=log(pos)/log(pri[i])-1;
return ans;
}
int main()
{
vis[1]=1;
for(int i=2;i<=1000000;i++)
{
if(!vis[i])
pri[++cnt]=i;
for(int j=1;j<=cnt&&i*pri[j]<=1000000;j++)
{
vis[i*pri[j]]=1;
if(i%pri[j]==0)
break;
}
}
scanf("%d",&n);
while(n--)
{
long long l,r;
scanf("%lld%lld",&l,&r);
printf("%lld\n",query(r)-query(l-1));
}
return 0;
}