新鲜到java（数组和素数）需要帮助解决问题

i have to have an array of 1000 numbers (1- 1000)and sort out the prime numbers and print just those from the array. i have to use 4 methods while doing this:

我必须有一个1000个数字(1- 1000)的数组,并整理素数并打印出数组中的数字。这样做时我必须使用4种方法:

//publicstaticvoidmain(String[] args) //calls on int[] a

// publicstaticvoidmain(String [] args)//调用int [] a

//publicstaticvoid init(int[] a)

// publicstaticvoid init(int [] a)

//publicstaticvoid findPrimes(int[] a)

// publicstaticvoid findPrimes(int [] a)

//publicstaticvoid printPrimes(int[] a)

// publicstaticvoid printPrimes(int [] a)

i have it almost done i think but i just cant quite get it to search and print the prime numbers, i keep printing the wrong values, sorry for the mess of code in advance i try to put side notes to keep track. ps. im very new and very bad at java

我觉得它几乎完成了我想但我只是不能让它搜索并打印素数,我一直打印错误的值,对不起提前代码的混乱,我试着把旁注留意。 PS。我非常新,非常糟糕的java

    class findPrimes {

    public static void main(String[] args) {

        int[]a = new int [1001];
        init(a);
        findPrimes(a);
        printPrimes(a);


    }

    public static void init(int[]a){        
        for(int i = 2; i < a.length; i++) {
            a[i] = 1;
            boolean isprime = true;
        //  System.out.println(i);
        }

    }


    public static void findPrimes(int[] a){
                for (int i = 2; i < a.length; i++){

                    }
                }       
        for (int j = 2*i; j <= a.length; j = j+i){
            int ind = j * i;
            if (ind>= a.length)
            a[i] = 0 ; 




    }
    }               
           }
    public static void printPrimes(int[] a){
            for(int i = 2; i < a.length; i++){
            if(a[i] == 1) {
                if (i%j == 0){
                    prime = false;
                    break;

                    System.out.print(i + ", ");
                }



    }
}   }

1 个解决方案

#1

Looks like you are trying to implement Sieve of Eratosthenes algorithm, but your code is a bit messy.

看起来你正在尝试实现Sieve of Eratosthenes算法,但你的代码有点乱。

Use this link >> please for explanations around the algorithm, it also includes implementation in Java, so solution will look like this:

使用此链接>>请关于算法的解释,它还包括Java实现,因此解决方案将如下所示:

public class FindPrimes {

    public static void main(String[] args) {
        runEratosthenesSieve(1000);
    }

    private static void runEratosthenesSieve(int upperBound) {
        int upperBoundSquareRoot = (int) Math.sqrt(upperBound);
        boolean[] isComposite = new boolean[upperBound + 1];
        for (int m = 2; m <= upperBoundSquareRoot; m++) {
            if (!isComposite[m]) {
                System.out.print(m + " ");
                for (int k = m * m; k <= upperBound; k += m) {
                    isComposite[k] = true;
                }
            }
        }

        for (int m = upperBoundSquareRoot; m <= upperBound; m++) {
            if (!isComposite[m]) {
                System.out.print(m + " ");
            }
        }
    }

}

If you want explanations around the mistakes in your code, we can discuss them too.

如果您想要解释代码中的错误,我们也可以讨论它们。

#1