Problem 2723(半素数)
题目定义了一种叫半素数的数：只要一个数能被分解成两个素数，那么这个数就是半素数。
Prime Number Definition
An integer greater than one is called a prime number if its only positive divisors (factors) are one and itself. For instance, 2, 11, 67, 89 are prime numbers but 8, 20, 27 are not.
Semi-Prime Number Definition
An integer greater than one is called a semi-prime number if it can be decompounded to TWO prime numbers. For example, 6 is a semi-prime number but 12 is not.
Your task is just to determinate whether a given number is a semi-prime number.
Input
There are several test cases in the input. Each case contains a single integer N (2 <= N <= 1,000,000)
Output
One line with a single integer for each case. If the number is a semi-prime number, then output "Yes", otherwise "No".
Sample Input
3
4
6
12
Sample Output
No
Yes
Yes
No
没什么好说的，解法很简单，解法如下：
#include <iostream>
#include <cmath>
using namespace std;
bool isprime(long test)
{
int i;
for(i=2;i<=sqrt((long double)test);i++)
{
if(test%i ==0)
return false;
}
return true;
}
bool isSemiPrime(long test)
{
int i;
for(i=2;i<=sqrt((long double)test);i++)
{
if(test%i ==0)
{
int temp = test/i;
return isprime(i) && isprime(temp);
}
}
return false;
}
int main()
{
long n;
while(cin>>n && n !=0)
{
if(isSemiPrime(n))
cout<<"Yes"<<endl;
else
cout<<"No"<<endl;
}
}
