AP Computer Science --- Haas --- RecursivePermutations

 
/**
*   This class generates permutations of a word.
*   
*   This class is complete and works as is.
*   
*   Your assignment is to trace through the program and 
*   hand in a "tree diagram" showing all of the calls to method perm.
*/
public class Permutations
{
    public static void perm(String prefix, String s) {
        int N = s.length();
        if (N == 0) {
            System.out.println(prefix);
        }
        else {
            for (int i = 0; i < N; i++) {
               perm(prefix + s.substring(i,i+1), s.substring(0, i) + s.substring(i+1, N));
            }
        }
    }
 
    public static void main(String[] args) 
    {
        perm("","abc");
    }
}