Permutations

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import java.util.*;

public class Main
{
  public static void main (String[]args)
  {
    List < String > list = singlePermutations ("aabb");
    for (String s:list)
      {
    System.out.println (s);
      }
  }

  public static List < String > singlePermutations (String s)
  {
    // Your code here!
    ArrayList < String > allPermutations = new ArrayList <> ();
    String[]letters = s.split ("");

    int permutationCount = 1;
    int length = s.length ();

    ArrayList < Integer > pList = new ArrayList <> ();
    pList.add (permutationCount);
    for (int i = 1; i <= s.length (); i++)
      {
    permutationCount *= i;
    pList.add (permutationCount);
      }

    String[][]permutations = new String[permutationCount][s.length ()];
    int amount=0;
    int repetitions=0;
    int totalRepetitions=0;
    int startRow=0;
    int column=0;
    try {
        for (int i = 0; i < length; i++){
            amount = pList.get(pList.size()-2-i);
            repetitions = pList.get(pList.size()-2)/amount;
            totalRepetitions = repetitions*length;
            startRow = 0;
            column = i;
            //System.out.println(String.format("Amount: %d - Repititions: %d - Total Repititions: %d", amount, repetitions, totalRepetitions));
            for (int j = 0; j < totalRepetitions; j++){
                for (int k = startRow; k < startRow+amount; k++){
                    while (permutations[k][column%length] != null){
                        column++;
                    }
                    permutations[k][column%length] = letters[i];
                }
                column++;
                startRow+=amount;
            }
        }
    } catch (Exception e) {
        System.out.println(String.format("Amount: %d - Repititions: %d - Total Repititions: %d - Start Row: %d - Column: %d", amount, repetitions, totalRepetitions, startRow, column));
    }

    StringBuilder sb;

    for (int i = 0; i < permutationCount; i++)
      {
    sb = new StringBuilder ("");
    for (int j = 0; j < length; j++)
      {
        sb.append (permutations[i][j]);
      }
      if(!allPermutations.contains(sb.toString ())){
        allPermutations.add (sb.toString ());
      }
      }

    boolean test = true;
    if (test) return allPermutations;

    ArrayList < String > singlePermutations = new ArrayList <> ();

    while (!allPermutations.isEmpty ())
      {
    singlePermutations.add (allPermutations.get (0));
    allPermutations.removeAll (singlePermutations);
      }

    return singlePermutations;
  }
}