public static void main(String[] args) { Scanner sc = new Scanner(System.in); String [] ops = sc.nextLine().split(" "); StringBuilder sb = new StringBuilder(); for (int i = 0; i < ops.length; i++) { ops[i]=sc.nextLine(); if (ops[i]=="[0-9]"){ sb.append(ops[i]); }else if (ops[i]=="+"){ sb.append((ops[i-1]+ops[i-2])); }else if (ops[i]=="C"){ sb.deleteCharAt(i-1); }else if (ops[i]=="D"){ sb.append((ops[i-1]+ops[i-1])); }else { System.out.println("-1"); } System.out.println(sb.toString()); } }；检查上面的代码，标出问题，并且优化下代码输出

在这个程序中，有以下两个问题：

1. 字符串比较应该使用equals方法，而不是==运算符。
2. 在处理加法、撤销和双倍运算时，应该先检查是否存在足够的操作数。

下面是修复了这些问题的代码：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] ops = sc.nextLine().split(" ");
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < ops.length; i++) {
            if (ops[i].matches("[0-9]+")) {
                sb.append(ops[i]);
            } else if (ops[i].equals("+")) {
                if (sb.length() < 2) {
                    System.out.println("-1");
                    return;
                }
                int a = Integer.parseInt(sb.substring(sb.length() - 2, sb.length() - 1));
                int b = Integer.parseInt(sb.substring(sb.length() - 1));
                sb.append(a + b);
            } else if (ops[i].equals("C")) {
                if (sb.length() < 1) {
                    System.out.println("-1");
                    return;
                }
                sb.deleteCharAt(sb.length() - 1);
            } else if (ops[i].equals("D")) {
                if (sb.length() < 1) {
                    System.out.println("-1");
                    return;
                }
                int a = Integer.parseInt(sb.substring(sb.length() - 1));
                sb.append(a * 2);
            } else {
                System.out.println("-1");
                return;
            }
            System.out.println(sb.toString());
        }
    }
}

优化输出：

在每次处理完操作后，输出当前的得分情况即可，不需要每次都输出所有的操作序列。修改后的代码如下：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] ops = sc.nextLine().split(" ");
        StringBuilder sb = new StringBuilder();
        int sum = 0;
        for (int i = 0; i < ops.length; i++) {
            if (ops[i].matches("[0-9]+")) {
                sb.append(ops[i]);
                sum += Integer.parseInt(ops[i]);
            } else if (ops[i].equals("+")) {
                if (sb.length() < 2) {
                    System.out.println("-1");
                    return;
                }
                int a = Integer.parseInt(sb.substring(sb.length() - 2, sb.length() - 1));
                int b = Integer.parseInt(sb.substring(sb.length() - 1));
                sb.append(a + b);
                sum += a + b;
            } else if (ops[i].equals("C")) {
                if (sb.length() < 1) {
                    System.out.println("-1");
                    return;
                }
                sum -= Integer.parseInt(sb.substring(sb.length() - 1));
                sb.deleteCharAt(sb.length() - 1);
            } else if (ops[i].equals("D")) {
                if (sb.length() < 1) {
                    System.out.println("-1");
                    return;
                }
                int a = Integer.parseInt(sb.substring(sb.length() - 1));
                sb.append(a * 2);
                sum += a * 2;
            } else {
                System.out.println("-1");
                return;
            }
            System.out.println(sum);
        }
    }
}