This is a recursive function to generate all permutations of a string in Java. For example, if “abc” is entered, the code will generate all permutations of length 1 to 3 characters: a, b, c, ab, ac, ba, bc, ca, cb, abc, acb, bac, bca, cab, cba.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 | import java.util.ArrayList; public class Permutation { private ArrayList permutations = null; private String characters = null; public Permutation(String characters) { if((characters == null) || ("").equals(characters.trim())) { characters = ""; } this.characters = characters; } public String getCharacters() { return characters; } public ArrayList getPermutations() { this.permutations = new ArrayList(); for(int j = 1; j <= getCharacters().length(); j++) { permute("",getCharacters(),j); } return this.permutations; } protected void permute(String prefix,String s,int length) { String word = null; for(int i = 0; i < s.length(); i++) { word = prefix+s.charAt(i); if(word.length() == length) { permutations.add(word); } else { if(i == 0) { permute(word,s.substring(i+1,s.length()),length); } else if(i == (s.length()-1)) { permute(word,s.substring(0,s.length()-1),length); } else { permute(word,(s.substring(0,i)+s.substring(i+1,s.length())),length); } } } return; } } |