java - My puzzle about getting a function to return a permutation array -


i want method returns permutations of input string. have searched internet , found of them similar robert sedgewick's code:http://introcs.cs.princeton.edu/java/23recursion/permutations.java.html

however, want return permutations, not print them. robert sedgewick's code copied here:

public class permutations {     // print n! permutation of characters of string s (in order)     public  static void perm1(string s) { perm1("", s); }     private static void perm1(string prefix, string s) {         int n = s.length();         if (n == 0) system.out.println(prefix);         else {             (int = 0; < n; i++)                perm1(prefix + s.charat(i), s.substring(0, i) + s.substring(i+1, n));         }     }     public static void main(string[] args) {        perm1("abcd");     } }

and code recoding robert sedgewick's myself below:

import java.util.arraylist;  public class test {     public static arraylist<string> permute(string prefix, string s){         int len = s.length();         arraylist<string> list = new arraylist<string>();         if(s.length() == 0)             list.add(prefix);         else             for(int = 0; < len; i++)                 permute(prefix + s.charat(i), s.substring(0, i) + s.substring(i+1, len));         return list;     }     public static void main(string[] args) {         string str = "abcd";         arraylist<string> array = permute("", str);         system.out.print(array.size());     } }

but code doesn't return permutations. returns nothing. don't know why. can me?

you need add result of permute method arraylist:

import java.util.arraylist;  public class test {     public static arraylist<string> permute(string prefix, string s){         int len = s.length();         arraylist<string> list = new arraylist<string>();         if(s.length() == 0)             list.add(prefix);         else             for(int = 0; < len; i++)                 list.addall(permute(prefix + s.charat(i), s.substring(0, i) + s.substring(i+1, len)));         return list;     }     public static void main(string[] args) {         string str = "abcd";         arraylist<string> array = permute("", str);         system.out.print(array.size());     } }

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