java 回溯+Set去重

用回溯思想做,结果用Set去重

import java.util.*;
public class Solution {
    Set<String> res = new HashSet<>();
    public ArrayList<String> Permutation(String str) {
         boolean[] visited = new boolean[str.length()];
         recursion(str,"",visited);
         ArrayList<String> list = new ArrayList<>(res);
         Collections.sort(list);
        return list;
    }
    public void recursion(String str,String current,boolean[] visited){
        if(str.length()==current.length()){
            res.add(current);
            return;
        }
        for(int i = 0;i<str.length();i++)
        {
          if(!visited[i]){
              current+=str.charAt(i);
              visited[i] = true;
              recursion(str,current,visited);
              current = current.substring(0,current.length()-1);
              visited[i] = false;
            }
        } 
    }
}