题解 | #字符串的排列#

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        ArrayList<String> ans=new ArrayList<>();
        String res=sc.nextLine();
        char[] arr=res.toCharArray();
        reverse(arr,0,arr.length-1,ans);
        HashSet<String> tmp=new HashSet<>(ans);
        ans.clear();
        for(String a:tmp){
            ans.add(a);
        }
        Collections.sort(ans);
         System.out.print(ans);
        
    }
    
    public static void reverse(char[] arr,int index,int len,ArrayList<String> ans){
        if(len==index){
            ans.add(change(arr));
           
        }
        for(int i=index;i<=len;i++){
            char tmp=arr[i];
            arr[i]=arr[index];
            arr[index]=tmp;
            reverse(arr,index+1,len,ans);
            tmp=arr[i];
            arr[i]=arr[index];
            arr[index]=tmp;
        }
    }
    private static String change(char[] arr){
        StringBuilder ans=new StringBuilder();
        for(char tmp:arr){
            ans.append(tmp);
        }
        return ans.toString();
    }
}