Generate all permutation of a string in recursion in java

Question

I would like to know how to create all permutation of a given string in a recursive way.

Lets say that String a = "abcdefghijklmnopqrstxyz";.

I would like to generate a string of length 5 (for example) from a using recursion,

meaning:

aaaaa
aaaab
aaaba
aaaca
zabfg

Thanks in advance.

This is the question...How to create the described permutations using recursion only. — Efi, Jun 11 '16 at 06:20
Along with that solution, only print out results of length 5 — OneCricketeer, Jun 11 '16 at 09:41
This solution is not what I'm looking for. I cannot use any for loops in this task. All other solutions that I saw in this website use for loops. — Efi, Jun 11 '16 at 10:45

score 1 · Answer 1 · answered Jun 11 '16 at 00:14

1

First, just store all the unique characters using a HashMap or so, then transfer them to a List, which we will call chars, for ease of use.

Your recursive method is building on a string. When that string reaches length 5, you are done, and you want to keep it. You can return the string or simply store it in a global list.

In this case, assume your list is called permutations.

void generatePermutation(String current) {
    if (current.length == 5) {
        permutations.add(current);
    } else {
        for (int i = 0; i < chars.size(); i++) {
            generatePermutation(current + chars.get(i));
        }
    }
}

answered Jun 11 '16 at 00:14

questioner and answerer

680
3
15

Thanks, but I'm not allowed to use for loop, only recursion.. – Efi Jun 11 '16 at 06:16
And I have to generate all possible permutations of length 5. In the example I gave there are 5^26 permutations. – Efi Jun 11 '16 at 06:25
It is impossible to do without a for loop. – questioner and answerer Jun 12 '16 at 04:10

Generate all permutation of a string in recursion in java

1 Answers1