Every combination of character array

Question

Having problems trying to show every combination of a character of array without repeating letters.

public static String[] getAllLists(String[] elements, int         


        

Answer 1

Here's an example implementation. Essentially it takes a String and iterates over every character, putting that character at the front. It then recurses on the remaining characters. That structure removes your issue of repeated letters, because the input to the recursion has removed the character you've already used.

I also stored results in a set to remove semantic equivalences. The input 'aab' can switch char 0 and char 1 but still be 'aab.' I used a TreeSet to preserve ordering for easier verification of the output, but HashSet would be faster.

  public static Set permute(String chars)
  {
    // Use sets to eliminate semantic duplicates (aab is still aab even if you switch the two 'a's)
    // Switch to HashSet for better performance
    Set set = new TreeSet();

    // Termination condition: only 1 permutation for a string of length 1
    if (chars.length() == 1)
    {
      set.add(chars);
    }
    else
    {
      // Give each character a chance to be the first in the permuted string
      for (int i=0; i

Example run:

  public static void main(String[] args)
  {
    for (String s : CharPermuter.permute("abca"))
    {
      System.out.println(s);
    }
  }

Generates:

aabc
aacb
abac
abca
acab
acba
baac
baca
bcaa
caab
caba
cbaa