Smart way to generate permutation and combination of String

Question

String database[] = {\'a\', \'b\', \'c\'};

I would like to generate the following strings sequence, based on given database.

Answer 1

Ok, so the best solution to permutations is recursion. Say you had n different letters in the string. That would produce n sub problems, one for each set of permutations starting with each unique letter. Create a method permutationsWithPrefix(String thePrefix, String theString) which will solve these individual problems. Create another method listPermutations(String theString) a implementation would be something like

void permutationsWithPrefix(String thePrefix, String theString) {
   if ( !theString.length ) println(thePrefix + theString);
   for(int i = 0; i < theString.length; i ++ ) {
      char c = theString.charAt(i);
      String workingOn = theString.subString(0, i) + theString.subString(i+1);   
      permutationsWithPrefix(prefix + c, workingOn);
   }
} 

void listPermutations(String theString) {
   permutationsWithPrefix("", theString);
}