题解 | #提取不重复的整数#

从尾部开始循环，利用HashSet检查是否重复

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        int len = str.length();
        Set<Character> set = new HashSet<>();
        char ch;
        for(int i=len-1;i>=0;i--){
            if(set.size()==10)break;
            ch = str.charAt(i);
            if(!set.contains(ch)){
                set.add(ch);
                System.out.print(ch);
            }
        }
    }
}