Find all combinations of a given set of numbers

Question

say I have a set of numbers \'0\', \'1\', \'2\', ..., \'9\'. I want to find all numbers that contain exactly one of each of the numbers in my set.

The problem is: Be

Answer 1

How many numbers, and which ones, aren't two questions. If you know which numbers, you know how many.

And the names of the numbers aren't very interesting. 1-3-14 or 0-1-2 or Foo-Bar-Baz - it is always the same problem, the same problem as the permutations of 0-1-2 and with an array, where to look up the result.

idx nums words
0   1     foo
1   3     bar
2   14    baz

The most convenient solution is, to write a generic Iterable. Then you can use the simplified for-loop, to access each permutation.

import java.util.*;

class PermutationIterator  implements Iterator > {

    private int  current = 0;
    private final long last;
    private final List  lilio;

    public PermutationIterator (final List  llo) {
        lilio = llo;
        long product = 1;
        for (long p = 1; p <= llo.size (); ++p) 
            product *= p; 
        last = product;
    }

    public boolean hasNext () {
        return current != last;
    }

    public List  next () {
        ++current;
        return get (current - 1, lilio);
    }

    public void remove () {
        ++current;
    }

    private List  get (final int code, final List  li) {
        int len = li.size ();
        int pos = code % len;
        if (len > 1) {
            List  rest = get (code / len, li.subList (1, li.size ()));
            List  a = rest.subList (0, pos);
            List  res = new ArrayList  ();
            res.addAll (a);
            res.add (li.get (0));
            res.addAll (rest.subList (pos, rest.size ()));
            return res;
        }
        return li;
    }
}

class PermutationIterable  implements Iterable > {

    private List  lilio; 

    public PermutationIterable (List  llo) {
        lilio = llo;
    }

    public Iterator > iterator () {
        return new PermutationIterator  (lilio);
    }
}

class PermutationIteratorTest {

    public static void main (String[] args) {
        List  la = Arrays.asList (new Integer [] {1, 3, 14});
        PermutationIterable  pi = new PermutationIterable  (la);
        for (List  lc: pi)
            show (lc);
    }

    public static void show (List  lo) {
        System.out.print ("(");
        for (Object o: lo)
            System.out.print (o + ", ");
        System.out.println (")");
    }
}