字符串的排列

class Solution {
    //全排列问题
    Set<List<Character>> res = new HashSet<>();
    public String[] permutation(String s) {
    char []strs =  s.toCharArray();
    int len = strs.length;
    boolean []used = new boolean[len];
    LinkedList<Character> list = new LinkedList<>();
    dfs(0,used,list,strs);
    String[] result = new String[res.size()];
    int top=0;
    for(List<Character> elem : res){
        String tmp = "";
      LinkedList<Character> e =  (LinkedList<Character>)elem;
      for(int i=0;i<len;i++){
          tmp+=e.get(i)+"";
      }
      result[top++] = tmp;
    }
    return result;
    }
    void dfs(int u,boolean []used,LinkedList list,char[] strs){
        if(u == strs.length){
            res.add(new LinkedList<>(list));
            return;
        }
        for(int i=0;i<strs.length;i++){
            if(!used[i]){
                used[i] = true;
                list.add(strs[i]);
                dfs(u+1,used,list,strs);
                used[i] = false;
                list.removeLast();

            }
        }
    }


}