检查给定的数字是否为素数？

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英文:

Check whether the given number is prime or not?

问题

这是我的代码。

  1. Scanner scan = new Scanner(System.in);
  2. int number = scan.nextInt();
  3. int[] arr = new int[number];
  4. for (int i = 0; i < number; i++) {
  5.     arr[i] = scan.nextInt();
  6. }
  8. for (int i = 0; i < number; i++) {
  9.     int num = arr[i];
  10.     for (int j = 2; j <= Math.sqrt(num); j++) {
  11.         if (num % j == 0 && num != 2) {
  12.             System.out.println(num + "不是质数");
  13.             break;
  14.         }
  15.     }
  16.     System.out.println(num + "是质数");
  17. }
英文:

I am trying to implement a code to check whether a given array of numbers is prime or not,

but when the number is not a prime number, the output displays "Prime" and "Not Prime" both answers. What is the mistake I did here and it is a pleasure to have an answer from you? Thank you in advance!

Here is my code.

  1.     Scanner scan = new Scanner(System.in);
  2.     int number = scan.nextInt();
  3.     int[] arr = new int[number];
  4.     for (int i = 0; i &lt; number; i++) {
  5.         arr[i] = scan.nextInt();
  7.     }
  9.     for (int i = 0; i &lt; number; i++) {
  10.         int num = arr[i];
  11.         for (int j = 2; j &lt;= Math.sqrt(num); j++) {
  12.             if (num % j == 0 &amp;&amp; num !=2) {
  13.                 System.out.println(num + &quot;Not prime&quot;);
  14.                 break;
  15.             }
  16.         }
  17.         System.out.println(num +&quot;Prime&quot;);
  18.     }

答案1

得分: 2

如果你对使你的代码更高效感兴趣，可以采用以下方法。

  1. int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
  2.                 15, 16, 17, 18, 19, 20 };
  3. for (int num : numbers) {
  4.     System.out.println(num + ((isPrime(num) ? " 是" : " 不是") + " 质数"));
  5. }		
  7. private static boolean isPrime(int num) {
  8.     // 两是质数
  9.     if (num == 2) {
  10.         return true;
  11.     }
  12.     // 数字小于等于1或任何偶数
  13.     // 数字（除2外）都不是质数
  14.     if (num <= 1 || num % 2 == 0) {
  15.         return false;
  16.     }
  17.     // 现在你可以检查奇数除数。
  18.     // 并从3开始每次增加2。
  19.     for (int i = 3; i <= Math.sqrt(num); i+=2) {
  20.         if (num % i == 0) {
  21.             return false;
  22.         }
  23.     }
  24.     return true;
  25. }
英文:

If you're interested in making your code a little more efficient you can go this route.

  1. int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
  2. 		15, 16, 17, 18, 19, 20 };
  3. for (int num : numbers) {
  4. 	System.out.println(num + ((isPrime(num) ? &quot; is&quot; : &quot; is not&quot;) + &quot; a prime&quot;));
  5. }		
  6. 	
  7. private static boolean isPrime(int num) {
  8. 	// two is a prime
  9.     if (num == 2) {
  10.        return true;
  11.     }
  12.     // numbers 1 or less or any even 
  13.     // number (sans 2) are not primes
  14.     if (num &lt;= 1 || num % 2 == 0) {
  15.         return false;
  16.     }
  17.     // Now you can check for odd divisors.
  18.     // and increment by 2 starting with 3.
  19.     for (int i = 3; i &lt;= Math.sqrt(num); i+=2) {
  20.         if (num % i == 0) {
  21.             return false;
  22.         }
  23.     }
  24.     return true;
  25. }

答案2

得分: 1

你应该记住这个数字是不是素数。你的代码没有这样做，因此两个打印语句都会被执行。

  1. Scanner scan = new Scanner(System.in);
  2. int number = scan.nextInt();
  3. int[] arr = new int[number];
  4. for (int i = 0; i < number; i++) {
  5.     arr[i] = scan.nextInt();
  6. }
  8. for (int i = 0; i < number; i++) {
  9.     int num = arr[i];
  10.     boolean isPrime = true;
  12.     for (int j = 2; j <= Math.sqrt(num); j++) {
  13.         if (num % j == 0 && num != 2) {
  14.             isPrime = false;
  15.             break;
  16.         }
  17.     }
  18.     
  19.     if (isPrime) {
  20.         System.out.println(num + "是素数");
  21.     } else {
  22.         System.out.println(num + "不是素数");
  23.     }
  24. }
英文:

You should remember whether the number was prime or not. Your code doesn't do that so both prints are reached.

  1. Scanner scan = new Scanner(System.in);
  2. int number = scan.nextInt();
  3. int[] arr = new int[number];
  4. for (int i = 0; i &lt; number; i++) {
  5.     arr[i] = scan.nextInt();
  7. }
  9. for (int i = 0; i &lt; number; i++) {
  10.     int num = arr[i];
  11.     boolean isPrime = true;
  13.     for (int j = 2; j &lt;= Math.sqrt(num); j++) {
  14.         if (num % j == 0 &amp;&amp; num !=2) {
  15.             isPrime = false;
  16.             break;
  17.         }
  18.     }
  19.     
  20.     if (isPrime) {
  21.         System.out.println(num +&quot;Prime&quot;);
  22.     } else {
  23.         System.out.println(num + &quot;Not prime&quot;);
  24.     }
  26. }

答案3

得分: 1

使用布尔值来跟踪数字是否为素数。开始时假设它为true（素数），如果发现不是素数，则将其设置为false。

  1. boolean isPrime = true;

然后，根据该布尔值确定消息。

  1. String message = isPrime ? "素数" : "非素数";
英文:

Use a boolean to track whether the number is prime. Assume it's true (prime) to begin with and set it false if it is discovered not to be prime.

  1. boolean isPrime = true;

Afterwards, determine the message based on that boolean.

  1. String message = isPrime ? &quot;Prime&quot; : &quot;Not prime&quot;;

答案4

得分: 0

你可以通过引入一个布尔变量来修复它，例如：

  1. for (int i = 0; i < number; i++) {
  2.     int num = arr[i];
  3.     boolean isPrime = true;
  4.     for (int j = 2; j <= Math.sqrt(num); j++) {
  5.         if (num % j == 0 && num != 2) {
  6.             isPrime = false;
  7.             break;
  8.         }
  9.     }
  10.     if (isPrime) {
  11.        System.out.println(num + "是质数");
  12.     } else {
  13.        System.out.println(num + "不是质数");
  14.     } 
  15. }
英文:

You can fix it for example by introducing a boolean variable:

  1.     for (int i = 0; i &lt; number; i++) {
  2.         int num = arr[i];
  3.         boolean isPrime = true;
  4.         for (int j = 2; j &lt;= Math.sqrt(num); j++) {
  5.             if (num % j == 0 &amp;&amp; num !=2) {
  6.                 isPrime = false;
  7.                 break;
  8.             }
  9.         }
  10.         if (isPrime) {
  11.            System.out.println(num +&quot;Prime&quot;);
  12.         } else {
  13.            System.out.println(num + &quot;Not prime&quot;);
  14.         } 
  15.     }

huangapple
  • 本文由 发表于 2020年4月8日 01:39:00
  • 转载请务必保留本文链接：https://go.coder-hub.com/61086061.html
  • java
  • primes
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