合成号码

原文:https://www.geeksforgeeks.org/composite-number/

一个复合数是一个非素数的正整数。换句话说，它有一个正除数，而不是一个或它本身。前几个合成数字是 4、6、8、9、10、12、14、15、16、18、20、……

  • 每一个大于 1 的整数要么是质数，要么是合数。
  • 第一个是一个单位，它既不是质数，也不是合成数。

如何检查一个给定的数是否是复合数？ 例:

Input : n = 21
Output: Yes
The number is a composite number!

Input : n = 11
Output : No

想法很简单，我们可以使用以下任何一种方法进行质数检查。我们只需要更改返回语句。返回真改为返回假，反之亦然。

下面代码中的优化学校方法讨论。

C++

// A optimized school method based C++ program to check
// if a number is composite.
#include <bits/stdc++.h>
using namespace std;

bool isComposite(int n)
{
    // Corner cases
    if (n <= 1)  return false;
    if (n <= 3)  return false;

    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n%2 == 0 || n%3 == 0) return true;

    for (int i=5; i*i<=n; i=i+6)
        if (n%i == 0 || n%(i+2) == 0)
           return true;

    return false;
}

// Driver Program to test above function
int main()
{
    isComposite(11)?  cout << " true\n": cout << " false\n";
    isComposite(15)?  cout << " true\n": cout << " false\n";
    return 0;
}

Java 语言(一种计算机语言，尤用于创建网站)

/// An optimized method based Java
// program to check if a number
// is Composite or not.
import java.io.*;

class Composite
{
    static boolean isComposite(int n)
    {
        // Corner cases
        if (n <= 1)
        System.out.println("False");

        if (n <= 3)
        System.out.println("False");

        // This is checked so that we can skip
        // middle five numbers in below loop
        if (n % 2 == 0 || n % 3 == 0) return true;

        for (int i = 5; i * i <= n; i = i + 6)
            if (n % i == 0 || n % (i + 2) == 0)
            return true;

        return false;
    }

    // Driver Program to test above function
    public static void main(String args[])
    {
        System.out.println(isComposite(11) ?
                       "true" : "false");

        System.out.println(isComposite(15) ?
                       "true" : "false");
    }
}

// This code is contributed by Anshika Goyal

Python 3

# A optimized school method based Python program to check
# if a number is composite.

def isComposite(n):

    # Corner cases
    if (n <= 1):
        return False
    if (n <= 3):
        return False

    # This is checked so that we can skip
    # middle five numbers in below loop
    if (n % 2 == 0 or n % 3 == 0):
        return True
    i = 5
    while(i * i <= n):

        if (n % i == 0 or n % (i + 2) == 0):
            return True
        i = i + 6

    return False

# Driver Program to test above function

print("true") if(isComposite(11)) else print("false")
print("true") if(isComposite(15)) else print("false")
# This code is contributed by Anant Agarwal.

C

// A optimized school method based C# program
// to check if a number is composite.
using System;

namespace Composite
{
public class GFG
{    

    public static bool isComposite(int n)
    {

    // Corner cases
    if (n <= 1) return false;
    if (n <= 3) return false;

    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n % 2 == 0 || n % 3 == 0) return true;

    for (int i = 5; i * i <= n; i = i + 6)

        if (n % i == 0 || n % (i + 2) == 0)
        return true;

    return false;
    }

    // Driver Code
    public static void Main()
    {

    if(isComposite(11)) Console.WriteLine("true");
    else Console.WriteLine("false");

    if(isComposite(15)) Console.WriteLine("true");
    else Console.WriteLine("false");
    }

}
}

// This code is contributed by Sam007

服务器端编程语言（Professional Hypertext Preprocessor 的缩写）

<?php
// A optimized school
// method based PHP
// program to check
// if a number is composite.

function isComposite($n)
{

    // Corner cases
    if ($n <= 1)
        return false;
    if ($n <= 3)
        return false;

    // This is checked so
    // that we can skip
    // middle five numbers
    // in below loop
    if ($n%2 == 0 || $n % 3 == 0)
        return true;

    for ($i = 5; $i * $i <= $n;
                   $i = $i + 6)
        if ($n % $i == 0 || $n % ($i + 2) == 0)
        return true;

    return false;
}

    // Driver Code
    if(isComposite(11))
        echo "true";
        else
        echo "false";
        echo"\n";
    if(isComposite(15))
        echo "true";
        else
        echo "false";
        echo"\n";

// This code is contributed by Ajit.
?>

java 描述语言

<script>

// A optimized school method based Javascript program to check
// if a number is composite.

function isComposite(n)
{
    // Corner cases
    if (n <= 1) return false;
    if (n <= 3) return false;

    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n%2 == 0 || n%3 == 0) return true;

    for (let i=5; i*i<=n; i=i+6)
        if (n%i == 0 || n%(i+2) == 0)
        return true;

    return false;
}

// Driver Program to test above function

    isComposite(11)? document.write(" true" + "<br>"): document.write(" false" + "<br>");
    isComposite(15)? document.write(" true" + "<br>"): document.write(" false" + "<br>");

// This code is contributed by Mayank Tyagi

</script>

输出:

false
true

复合数字编程

参考: https://en.wikipedia.org/wiki/Composite_number 本文由 Ajay Puri 供稿。如果你喜欢 GeeksforGeeks 并想投稿，你也可以用contribute.geeksforgeeks.org写一篇文章或者把你的文章邮寄到 contribute@geeksforgeeks.org。看到你的文章出现在极客博客主页上，帮助其他极客。 如果发现有不正确的地方，或者想分享更多关于上述话题的信息，请写评论。

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