generating Variations without repetitions / Permutations in java

Question

I have to generate all variations without repetitions made of digits 0 - 9.

Length of them could be from 1 to 10. I really don\'t know how to solve it, especially ho

Answer 1

There is one solution which is not from mine, but it is very nice and sophisticated.

    package permutations;

import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;

/**
 * @author Vladimir Hajek
 *
 */
public class PermutationSimple {
    private static final int MAX_NUMBER = 3;

    Set results = new HashSet<>(0);

    /**
     * 
     */
    public PermutationSimple() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @param availableNumbers
     * @return
     */
    public static List generatePermutations(Set availableNumbers) {
        List permutations = new LinkedList<>();

        for (Integer number : availableNumbers) {
            Set numbers = new HashSet<>(availableNumbers);
            numbers.remove(number);

            if (!numbers.isEmpty()) {
                List childPermutations = generatePermutations(numbers);
                for (String childPermutation : childPermutations) {
                    String permutation = number + childPermutation;
                    permutations.add(permutation);
                }
            } else {
                permutations.add(number.toString());
            }
        }

        return permutations;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        Set availableNumbers = new HashSet<>(0);

        for (int i = 1; i <= MAX_NUMBER; i++) {
            availableNumbers.add(i);
        }

        List permutations = generatePermutations(availableNumbers);
        for (String permutation : permutations) {
            System.out.println(permutation);
        }

    }
}

I think, this is the excellent solution.