partner_program/src/main/java/com/example/myapp/service/PrimaryQueSeting.java

// PrimaryQueSeting.java
package com.example.myapp.service;

import com.example.myapp.model.Expression;

public class PrimaryQueSeting extends AbstractQuestionSeting {

  @Override
  public Expression setQuestion(int count) {
    if (count == 1) {
      String expr = getRandomNumber();
      return new Expression(expr, parseNumber(expr), null);
    }

    int leftCount = 1 + rand.nextInt(count - 1);
    int rightCount = count - leftCount;
    Expression left = setQuestion(leftCount);
    Expression right = setQuestion(rightCount);

    String op = getRandomOperator();

    // 处理除数为0的情况
    while (op.equals("/") && Math.abs(right.value) < 1e-10) {
      right = setQuestion(rightCount);
    }

    // 确保减法结果不为负数
    if (op.equals("-") && left.value < right.value) {
      Expression temp = left;
      left = right;
      right = temp;
    }

    String leftExpr = addParenthesesIfNeeded(left, op, false);
    String rightExpr = addParenthesesIfNeeded(right, op, true);

    double value = switch (op) {
      case "+" -> left.value + right.value;
      case "-" -> left.value - right.value;
      case "*" -> left.value * right.value;
      case "/" -> left.value / right.value;
      default -> 0;
    };

    return new Expression(leftExpr + " " + op + " " + rightExpr, value, op);
  }

  @Override
  public String addParenthesesIfNeeded(Expression child, String parentOp, boolean isRightChild) {
    if (child.mainOperator == null) {
      return child.expression;
    }

    int parentPriority = getPriority(parentOp);
    int childPriority = getPriority(child.mainOperator);

    if (childPriority < parentPriority) {
      return "(" + child.expression + ")";
    }

    if (isRightChild && (parentOp.equals("-") || parentOp.equals("/"))) {
      if (parentPriority == childPriority) {
        return "(" + child.expression + ")";
      }
    }

    return child.expression;
  }
}