题解 | #提取不重复的整数#

import java.util.HashSet;
import java.util.Scanner;

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