题解 | #字符串的排列# 递归法

import java.util.*;
public class Solution {
  ArrayList<String> ans=new ArrayList<>();
    boolean[]vis;
    public ArrayList<String> Permutation(String str) {
        char[]arr=str.toCharArray();
        Arrays.sort(arr);
        vis=new boolean[arr.length];
        dfs(arr,new StringBuilder());
        return ans;
    }

    private void dfs(char[] arr, StringBuilder stringBuilder) {
    if(stringBuilder.length()==arr.length)
    {
        ans.add(stringBuilder.toString());
        return;
    }
    
        for (int i = 0; i < arr.length; i++) {
    if(vis[i])
        continue;
   if(i>0&&!vis[i-1]&&arr[i]==arr[i-1]) continue;
    vis[i]=true;
    stringBuilder.append(arr[i]);
    dfs(arr,stringBuilder);
    vis[i]=false;
    stringBuilder.deleteCharAt(stringBuilder.length()-1);
        }
    }
}