Permutation of an array, with repetition, in Java

Question

There are some similar questions on the site that have been of some help, but I can\'t quite nail down this problem, so I hope this is not repetitive.

This is a home

Answer 1

I use this java realization of permutations with repetitions. A~(n,m): n = length of array, m = k. m can be greater or lesser then n.

public class Permutations {


    static void permute(Object[] a, int k, PermuteCallback callback) {
        int n = a.length;

        int[] indexes = new int[k];
        int total = (int) Math.pow(n, k);

        Object[] snapshot = new Object[k];
        while (total-- > 0) {
            for (int i = 0; i < k; i++){
                snapshot[i] = a[indexes[i]];
            }
            callback.handle(snapshot);

            for (int i = 0; i < k; i++) {
                if (indexes[i] >= n - 1) {
                    indexes[i] = 0;
                } else {
                    indexes[i]++;
                    break;
                }
            }
        }
    }

    public static interface PermuteCallback{
        public void handle(Object[] snapshot);
    };

    public static void main(String[] args) {
        Object[] chars = { 'a', 'b', 'c', 'd' };
        PermuteCallback callback = new PermuteCallback() {

            @Override
            public void handle(Object[] snapshot) {
                for(int i = 0; i < snapshot.length; i ++){
                    System.out.print(snapshot[i]);
                }
                System.out.println();
            }
        };
        permute(chars, 8, callback);
    }

}

Example output is

aaaaaaaa
baaaaaaa
caaaaaaa
daaaaaaa
abaaaaaa
bbaaaaaa
...
bcffffdffffd
ccffffdffffd
dcffffdffffd
affffdffffdd
bffffdffffdd
cffffdffffdd
ffffdffffffffd