在一次正确的迭代后停止内部循环

Question

代码中的问题出在 goldbach 方法中。我想在最内层循环找到一对数字后停止内层两个循环的迭代，但我不知道如何退出这两个循环。换句话说，我只想为最外层 for 循环创建的每个 i 整数找到一对，然后继续寻找下一个整数 i.

下面是我的代码：

import java.util.Arrays;
import java.awt.List;
import java.util.ArrayList;

// finding prime numbers using sieve of Eratosthenes and golbach's conjecture
public class Test {
    public static void main(String[] args) {

        int[] num = new int[1000000];

        for (int i = 2; i <= num.length; i++) {
            num[i - 1] = i;
        }
        Test.sieve(num);


        Test.goldbach(num);
    }
    public static void sieve(int[] array) {

        for (int i = 2; i < Math.sqrt(array.length); i++) {
            if (array[i - 1] == 0) {
                continue;
            }
            for (int j = 2 * i; j <= array.length; j += i) {
                array[j - 1] = 0;
            }
        }

        for (int i = 0; i < array.length; i++) {
            if (array[i] != 0) {
                //System.out.print(array[i] + " ");
            }
        }
        //System.out.println(Arrays.toString(array));
    }


    public static void goldbach(int[] array) {
        for (int i = 2; i <= 1000000; i += 2) { //to go through every even integer
            for (int j = 0; j <= i; j++) {
                for (int k = 0; k <= i; k++) {
                    System.out.println("two prime numbers that add to " + i + " are " + array[j] + " and " + array[k]);
                    break;
                }
            }
        }
    }
}
}

Answer 1

您可以在第二个循环中设置 j 的值。例如

for (int i = 2; i <= 1000000; i += 2) { //to go through every even integer
    for (int j = 0; j <= i; j++) { 
        for (int k = 0; k <= i; k++) {
                System.out.println("two prime numbers that add to " + i + " are " + array[j] + " and "  + array[k]);
                j = i + 1; // This will end the outer loop as well.
                break;
            }
        }
    }
}

Answer 2

使用标签打破（或继续）内部循环以外的循环：

    found:
    for (int j = 0; j <= i; j++) { 
        for (int k = 0; k <= i; k++) {
                System.out.println("two prime numbers that add to " + i + " are " + array[j] + " and "  + array[k]);
                break found;
            }
        }
    }

或使用其他方法和 return - 如果新方法有自己明确的功能（和更好名称）

public static void goldbach(int[] array) {
    for (int i = 2; i <= 1000000; i += 2) { //to go through every even integer
        primeAdd(i);
    }
}

private static void primeAdd(int i) {
    for (int j = 0; j <= i; j++) { 
        for (int k = 0; k <= i; k++) {
            System.out.println("two prime numbers that add to " + i + " are " + array[j] + " and "  + array[k]);
            return;
        }
    }
}

但是，正如 bureaquete 已经评论的那样，不需要内部循环，因为它总是被终止。

在一次正确的迭代后停止内部循环

Stopping an inner loop after one correct iteration

java

loops

for-loop

break