Permutation algorithm for array of integers in Java

Question

I have a working example to generate all char permutations in a String as below:

static ArrayList permutations(String s) {
        if (s == nul         


        

Answer 1

I've written that code some time ago, and edited a bit to match your requests. I hope it works.

static ArrayList permutations(String s) {
    ArrayList ret = new ArrayList();
    permutation(s.toCharArray(), 0, ret);
    return ret;
}

public static void permutation(char[] arr, int pos, ArrayList list){
    if(arr.length - pos == 1)
        list.add(new String(arr));
    else
        for(int i = pos; i < arr.length; i++){
            swap(arr, pos, i);
            permutation(arr, pos+1, list);
            swap(arr, pos, i);
        }
}

public static void swap(char[] arr, int pos1, int pos2){
    char h = arr[pos1];
    arr[pos1] = arr[pos2];
    arr[pos2] = h;
}

UPDATE
I just tried it on ideone.com. It seems to work. You're welcome. :)

UPDATE 2
It should basically be the same code with arrays of int's:

static ArrayList permutations(int[] a) {
    ArrayList ret = new ArrayList();
    permutation(a, 0, ret);
    return ret;
}

public static void permutation(int[] arr, int pos, ArrayList list){
    if(arr.length - pos == 1)
        list.add(arr.clone());
    else
        for(int i = pos; i < arr.length; i++){
            swap(arr, pos, i);
            permutation(arr, pos+1, list);
            swap(arr, pos, i);
        }
}

public static void swap(int[] arr, int pos1, int pos2){
    int h = arr[pos1];
    arr[pos1] = arr[pos2];
    arr[pos2] = h;
}

UPDATE 3
Works with int's too: http://ideone.com/jLpZow