10.20

package qixun;

import java.util.Random;

public class Grade3QuestionGenerator extends Grade2QuestionGenerator {
    public Grade3QuestionGenerator() {
        this.operandCount = 4; // 操作数不超过4个
        this.maxOperandValue = 1000; // 操作数范围不超过1000
    }

    @Override
    public String getQuestion() {
        Random random = new Random();
        StringBuilder question = new StringBuilder();

        // 生成最多4个操作数的表达式
        for (int i = 0; i < operandCount - 1; i++) {
            int operand = random.nextInt(maxOperandValue) + 1;
            String operator = generateOperator(); // 调用父类的 generateOperator()
            question.append(operand).append(" ").append(operator).append(" ");
        }
        question.append(random.nextInt(maxOperandValue) + 1); // 最后一个操作数

        return question.toString();
    }

    @Override
    public double getAnswer(String question) {
        double result = super.getAnswer(question);
        return result;
    }
}

package qixun;

import java.util.Random;

public class Grade4QuestionGenerator extends Grade3QuestionGenerator {
    public Grade4QuestionGenerator() {
        this.operandCount = 5;
    }

    @Override
    public String getQuestion() {
        Random random = new Random();
        StringBuilder question = new StringBuilder();

        // 可能加入括号
        boolean useBrackets = random.nextBoolean();
        if (useBrackets) {
            question.append("(");
        }

        for (int i = 0; i < operandCount - 1; i++) {
            int operand = random.nextInt(maxOperandValue) + 1;
            String operator = generateOperator();
            question.append(operand).append(" ").append(operator).append(" ");

            // 添加括号
            if (useBrackets && i == 2) {
                question.append("(").append(random.nextInt(maxOperandValue) + 1).append(") ");
                useBrackets = false; // 防止括号重复使用
            }
        }
        question.append(random.nextInt(maxOperandValue) + 1); // 最后一个操作数

        if (useBrackets) {
            question.append(")"); // 如果还未关闭括号，添加关闭括号
        }

        return question.toString().trim(); // 去掉多余空格
    }
}