检查数字是否为半素数

给定正整数n。查找数字是否为半素数。如果number是半素数，则输出True ，否则返回False 。半素数是一个自然数，它是两个素数的乘积。
例子 ：

Input: 6
Output: True
Explanation
6 is a semiprime number as it is a
product of two prime numbers 2 and 3.

Input: 9
Output: True

Input: 8
Output: False

该方法很简单，将给定数字除以数字的除数就可以分解出复合数字。同时不断更新素数计数变量。

C++

// C++ Program to check whether
// number is semiprime or not
#include 
using namespace std;
 
// Utility function to check whether
// number is semiprime or not
int checkSemiprime(int num)
{
    int cnt = 0;
 
    for (int i = 2; cnt < 2 && i * i <= num; ++i)
        while (num % i == 0)
            num /= i, ++cnt; // Increment count
                             // of prime numbers
 
    // If number is greater than 1, add it to
    // the count variable as it indicates the
    // number remain is prime number
    if (num > 1)
        ++cnt;
 
    // Return '1' if count is equal to '2' else
    // return '0'
    return cnt == 2;
}
 
// Function to print 'True' or 'False'
// according to condition of semiprime
void semiprime(int n)
{
    if (checkSemiprime(n))
        cout << "True\n";
    else
        cout << "False\n";
}
 
// Driver code
int main()
{
    int n = 6;
    semiprime(n);
    n = 8;
    semiprime(n);
    return 0;
}
 
// This code is contributed by rutvik_56.

C

// C Program to check whether
// number is semiprime or not
#include 
 
// Utility function to check whether
// number is semiprime or not
int checkSemiprime(int num)
{
    int cnt = 0;
 
    for (int i = 2; cnt < 2 && i * i <= num; ++i)
        while (num % i == 0)
            num /= i, ++cnt; // Increment count
                             // of prime numbers
 
    // If number is greater than 1, add it to
    // the count variable as it indicates the
    // number remain is prime number
    if (num > 1)
        ++cnt;
 
    // Return '1' if count is equal to '2' else
    // return '0'
    return cnt == 2;
}
 
// Function to print 'True' or 'False'
// according to condition of semiprime
void semiprime(int n)
{
    if (checkSemiprime(n))
        printf("True\n");
    else
        printf("False\n");
}
 
// Driver code
int main()
{
    int n = 6;
    semiprime(n);
 
    n = 8;
    semiprime(n);
    return 0;
}

Java

// Java Program to check whether
// number is semiprime or not
class GFG{
     
    // Utility function to check whether
    // number is semiprime or not
    static int checkSemiprime(int num)
    {
        int cnt = 0;
     
        for (int i = 2; cnt < 2 &&
                     i * i <= num; ++i)
                      
            while (num % i == 0){
                num /= i;
                 
                // Increment count
                // of prime numbers
                ++cnt;
                }
     
        // If number is greater than 1,
        // add it to the count variable
        // as it indicates the number
        // remain is prime number
        if (num > 1)
            ++cnt;
     
        // Return '1' if count is equal
        // to '2' else return '0'
        return cnt == 2 ? 1 : 0;
    }
     
    // Function to print 'True' or 'False'
    // according to condition of semiprime
    static void semiprime(int n)
    {
        if (checkSemiprime(n) != 0)
            System.out.printf("True\n");
        else
            System.out.printf("False\n");
    }
     
    // Driver code
    public static void main(String[] args)
    {
        int n = 6;
        semiprime(n);
     
        n = 8;
        semiprime(n);
    }
}
 
// This code is contributed by
// Smitha Dinesh Semwal

Python3

# Python Program to check whether
# number is semiprime or not
import math
# Utility function to check whether
# number is semiprime or not
def checkSemiprime(num):
    cnt = 0
 
    for i in range(2, int(math.sqrt(num)) + 1):
        while num % i == 0:
            num /= i
            cnt += 1 # Increment count
                    # of prime number
 
        # If count is greater than 2,
        # break loop
        if cnt >= 2:
            break
    # If number is greater than 1, add it to
    # the count variable as it indicates the
    # number remain is prime number
    if(num > 1):
        cnt += 1
 
    # Return '1' if count is equal to '2' else
    # return '0'
    return cnt == 2
 
# Function to print 'True' or 'False'
# according to condition of semiprime
def semiprime(n):
    if checkSemiprime(n) == True:
        print("True")
    else:
        print("False")
 
# Driver code
n = 6
semiprime(n)
 
n = 8
semiprime(n);

C#

// C# Program to check whether
// number is semiprime or not
using System;
class GFG{
     
    // Utility function to check whether
    // number is semiprime or not
    static int checkSemiprime(int num)
    {
        int cnt = 0;
     
        for (int i = 2; cnt < 2 &&
                    i * i <= num; ++i)
                     
            while (num % i == 0){
                num /= i;
                 
                // Increment count
                // of prime numbers
                ++cnt;
                }
     
        // If number is greater than 1,
        // add it to the count variable
        // as it indicates the number
        // remain is prime number
        if (num > 1)
            ++cnt;
     
        // Return '1' if count is equal
        // to '2' else return '0'
        return cnt == 2 ? 1 : 0;
    }
     
    // Function to print 'True' or 'False'
    // according to condition of semiprime
    static void semiprime(int n)
    {
        if (checkSemiprime(n) != 0)
            Console.WriteLine("True");
        else
            Console.WriteLine("False");
    }
     
    // Driver code
    public static void Main()
    {
        int n = 6;
        semiprime(n);
     
        n = 8;
        semiprime(n);
    }
}
 
// This code is contributed by vt_m.

PHP

 1)
        ++$cnt;
 
    // Return '1' if count is
    // equal to '2'
    // else return '0'
    return $cnt == 2;
}
 
// Function to print 'True' or 'False'
// according to condition of semiprime
function semiprime($n)
{
    if (checkSemiprime($n))
        echo "True\n";
    else
        echo "False\n";
}
 
// Driver code
$n = 6;
semiprime($n);
 
$n = 8;
semiprime($n);
 
// This code is contributed by anuj_67.
?>

Javascript

 
// JavaScript Program to check whether
// number is semiprime or not
 
    // Utility function to check whether
    // number is semiprime or not
    function checkSemiprime(num)
    {
        let cnt = 0;
      
        for (let i = 2; cnt < 2 &&
                     i * i <= num; ++i)
                       
            while (num % i == 0){
                num /= i;
                  
                // Increment count
                // of prime numbers
                ++cnt;
                }
      
        // If number is greater than 1,
        // add it to the count variable
        // as it indicates the number
        // remain is prime number
        if (num > 1)
            ++cnt;
      
        // Return '1' if count is equal
        // to '2' else return '0'
        return cnt == 2 ? 1 : 0;
    }
      
    // Function to print 'True' or 'False'
    // according to condition of semiprime
    function semiprime(n)
    {
        if (checkSemiprime(n) != 0)
            document.write("True" + "<br/>");
        else
            document.write("False"  + "<br/>");
    }
      
 
// Driver code   
          
        let n = 6;
        semiprime(n);
      
        n = 8;
        semiprime(n);
                       

输出 ：

True
False

时间复杂度： O( $\sqrt n$ )
辅助空间： O(1)
参考： https ： //en.wikipedia.org/wiki/Semiprime