java - 如何获得从扫描仪输入到阵列的所有排列？

Question

我正在尝试查找来自扫描仪的 PIN 码的所有排列。到目前为止，我已经知道了这一点，我想它会设置一个带有自定义数字的数组。我怎样才能得到这段代码来向我展示所有可能的选项？请记住，我是 Java 的新手，所以简单的解释是最好的。谢谢

import java.util.Arrays;
import java.util.Scanner;

public class Methods {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        int[] arr = new int[3];

        Scanner sc = new Scanner(System.in);
        System.out.println("Please enter first digit: ");
        arr[0] = sc.nextInt();
        System.out.println("Please enter second digit: ");
        arr[1] = sc.nextInt();
        System.out.println("Please enter third digit: ");
        arr[2] = sc.nextInt();
        System.out.println("Please enter fourth digit: ");
        arr[3] = sc.nextInt();

        System.out.println(Arrays.toString(arr));
        }
    }

Answer 1

嘿，您可以使用以下代码创建一个长度为 n 的数组并计算排列:

public static void main(String[] args) {

  Scanner sc = new Scanner(System.in);
  System.out.print("please enter the length of you array: "); // 4 if you want a 4 digit pincode
  int length = sc.nextInt();

  int[] arr = new int[length];

  for (int i = 0; i < length; i++) {
    System.out.printf("Please enter a value for digit #%s: ", i);
    arr[i] = sc.nextInt();
  }

  StringBuilder bldr = new StringBuilder();
  Arrays.stream(arr).forEach(bldr::append);
  permutation(bldr.toString());
}

public static void permutation(String str) {
    permutation("", str);
}

private static void permutation(String prefix, String str) {
  int n = str.length();
  if (n == 0)
    System.out.println(prefix);
  else {
    for (int i = 0; i < n; i++)
      permutation(prefix + str.charAt(i), str.substring(0, i) + str.substring(i + 1, n));
  }
}

同时检查 this question有关排列的更多信息。