题解 | 表示数字|StringBuilder

import java.util.Scanner;

// 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);
        String s = in.nextLine();
        StringBuilder sbr = new StringBuilder();
        boolean isPreDigit = false;
        for(int i = 0;i<s.length();i++) {
            boolean isDigit = Character.isDigit(s.charAt(i));
            if(!isPreDigit && isDigit || !isDigit && isPreDigit) {
                sbr.append('*');
            }
            isPreDigit = isDigit;
            sbr.append(s.charAt(i));
        }
        if(isPreDigit) {
            sbr.append('*');
        }

        System.out.println(sbr.toString());
    }
}