How to get all the possible sequences of x characters from a string of n characters in java

Question

I am playing with Java and my problem is the following:

I have a string of n characters, eg abcd, how can i get all the possible sequences of x characters in this string? with "sequences" i mean that I am interested ONLY in those combinations that respect the order of the characters in the original string.

So for instance if I am looking for 2 characters sequences in the string abcd I would like to obtain only

ab, ac, ad, bc, bd, cd.

I am not interested in all the other possible combinations (such as da, cb etc), because they do not respect the order of the characters in the original string.

Any suggestion?

Answer 1

This is a combination without repetition problem. There are plenty of implementations around the Internet, you can find one in this class .

Answer 2

The problem is solvable with two loops. What have you done so far to solve it on your own?

    public static void print(String str) {
        for (int i = 0; i < str.length(); i++) {
           char curChar = str.charAt(i);
           for (int j = i + 1; j < str.length(); j++) {
                char otherChar = str.charAt(j);
                System.out.println(new String(new char[] { curChar, otherChar }));
            }
        }
    }

Answer 3

Take a look at this:

TreeSet<String> set = new TreeSet<String>();
final String placeHolder = "ignore me 'cause toElement parameter of subSet() is exclusive";
    set.add("a");
    set.add("b");
    set.add("c");
    set.add("d");
    set.add(placeHolder);
    for (String ch : set) {
        Set<String> subSet = set.subSet(ch, placeHolder);
        if (subSet.size() > 1) {
            for (String subCh : subSet) {
                if (!ch.equals(subCh)) {
                    System.out.println(ch + subCh);
                }
            }
        }
    }