题解 | #提取不重复的整数#

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String st = sc.nextLine();
        sc.close();

        StringBuilder sb = new StringBuilder(st);
        st = sb.reverse().toString();//翻转
        char[] chars = st.toCharArray();
        TreeSet<Character> tree = new TreeSet();//去重后的数字保留在一个集合

        ArrayList<Character> list = new ArrayList();
        for(int i = 0; i<chars.length; i++){
            if(!tree.contains(chars[i])){
                list.add(chars[i]);//不在集合中的数字加入目标数组
            }
            tree.add(chars[i]);//补充集合
        }
        StringBuilder sb2 = new StringBuilder();//打印list即可
        for(int i = 0; i<list.size(); i++){
            sb2.append(list.get(i));
        } 
        System.out.println(sb2.toString());
        
    }
}