避免打印重复

Question

I wish to generate result that displaying different distinct/unique combinations of numbers.

For eg: if number is 4 digit ie: 4789 then output will be in format of 478,789,489,479 (in increasing order only.) My code is:

import java.util.Arrays;
import java.util.HashSet;
import java.util.Random;
import java.util.Scanner;

public class Permutation{
    static void permute(int[] a, int k) {
        int temp;
        if (k == a.length) {
            for (int i = 0; i < a.length - 1; i++) {
                for (int j = i + 1; j < a.length - 1; j++) {
                     if (a[i] > a[j]) {
                        temp = a[i];
                        a[i] = a[j];
                        a[j] = temp;
                     }
                  }
            System.out.print(a[i]);
            }
        System.out.println();
        } else {
            int tempLength = (a.length);
            for (int i = k; i < tempLength; i++) {
                temp = a[k];
                a[k] = a[i];
                a[i] = temp;
                permute(a, k + 1);
            }
        }
    }

    public static void main(String args[]) {

        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the length of list: ");
        int N = sc.nextInt();
        int[] sequence = new int[N];
        System.out.println("---------");
        for (int i = 0; i < N; i++)
            {
        sequence[i] = sc.nextInt();
            }
        System.out.println("The original sequence is: ");
        for (int i = 0; i < N; i++){
        System.out.print(sequence[i] + " ");
        System.out.println("\nThe permuted sequences are: ");
        permute(sequence, 0);
        sc.close();
    }}

Output of above program is:

Enter the length of list: 4
---------
1
2
7
8
The original sequence is: 
1 2 7 8 

The permuted sequences are: 

127,128,128,127,178,127,127,128,128,127,178,127,
127,128,128,127,178,127,278,127,127,128,178,127

So this result displays some duplicates elements. I want to avoid displaying such duplicate elements in array. In above code I'm expecting as output:127,128,178,278 Help, thank you in advance.

Answer 1

You can use StringBuilder :

private static String[] getDigitsArray(String str) {
    StringBuilder sb = new StringBuilder(str);
    sb.deleteCharAt(3).append(",")
            .append(new StringBuilder(str).deleteCharAt(0)).append(",")
            .append(new StringBuilder(str).deleteCharAt(1)).append(",")
            .append(new StringBuilder(str).deleteCharAt(2));
    return sb.toString().split(",");
}

Simple use:

String[] array = getDigitsArray("4789");
System.out.println("Result: "+Arrays.toString(array));

And it is the result:

Result: [478, 789, 489, 479]

For every 4 digits string you can use the code above, it will return an array which has for elements inside, and then you can do what you want with.