使用stream流 ,比其他方法复杂点,但是比较清晰。时间复杂度和空间复杂度都不是太好

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        char[] cList = scan.nextLine().toCharArray();
        List<String> list =new ArrayList();
        for (int i=0; i < cList.length; i++){
            list.add(String.valueOf(cList[i]));
        }
        Collections.reverse(list);
        list = list.stream().distinct().collect(Collectors.toList());
        
        for(String a:list){
            System.out.print(a);
        }
        }
}