Code for Variations with repetition (combinatorics)?

问题

Does anyone have Java code for generating all VARIATIONS WITH REPETITION?

There are plenty of permutation and combination examples available, and variations must be the easiest one... It feels stupid to waste time to reinvent the wheel (it must be plenty of code written for this).

An example of VARIATIONS WITH REPETITION could be like this:

(tupletSize=3, input= A, B)
AAA, AAB, ABA, BAA, ABB, BAB, BBA, BBB

Thanks!

回答1:

This works as is, and it's the easiest for you to study.

public class Main {
    public static void main(String args[]) {
        brute("AB", 3, new StringBuffer());
    }
    static void brute(String input, int depth, StringBuffer output) {
        if (depth == 0) {
            System.out.println(output);
        } else {
            for (int i = 0; i < input.length(); i++) {
                output.append(input.charAt(i));
                brute(input, depth - 1, output);
                output.deleteCharAt(output.length() - 1);
            }
        }
    }
}

回答2:

public class Main {

    public static void main(String[] args) throws IOException {
        LinkedList<char[]> items = new LinkedList<char[]>();
        char[] item = new char[3];
        char[] input = {'A', 'B'};
        rep(items, input, item, 0);


        for (char[] rep : items) {
            System.out.println(rep);
        }
    }

    private static void rep(LinkedList<char[]> reps, char[] input, char[] item, int count){
        if (count < item.length){
            for (int i = 0; i < input.length; i++) {
                item[count] = input[i];
                rep(reps, input, item, count+1);
            }
        }else{
            reps.add(item.clone());
        }
    }

}

produces following output: AAA AAB ABA ABB BAA BAB BBA BBB

watch out for stack overflows with big tupleSize. recursive algorithms (like this one) are usually slower than iterative versions but they are very handy to code.

回答3:

How to write a brute-force password cracker

While this is no Java implementation, the part doing the permutations should be quite easy to port in Java.

I ported it to C with no knowledge of Python, and it worked like a charm.

回答4:

You can use the principle of n-ary Gray code

http://en.wikipedia.org/wiki/Gray_code#Constructing_an_n-bit_Gray_code

来源：https://stackoverflow.com/questions/2366074/code-for-variations-with-repetition-combinatorics