题解 | #提取不重复的整数#

import java.util.Scanner; 

import java.util.HashSet;
import java.util.Stack;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        String ne = "";
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int a = in.nextInt();
            ne = String.valueOf(a);
        }
        Stack<String> stack =new Stack<>();
        HashSet<String> seth = new HashSet<>();
        for(int a =0;a<ne.length();a++){
            String c = ne.substring(a,a+1);
            stack.push(c);
        }
        while(!stack.isEmpty()){
            String df = stack.pop();
            if(!seth.contains(df)){
                seth.add(df);
                System.out.print(df);
            }
        }
    }
}