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@ -1,230 +1,151 @@
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import java.util.Random;
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/**
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* 小学题目生成策略实现类。
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*
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* <p>随机生成包含加、减、乘、除运算的表达式，保证符合题目要求。
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*/
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public class ElementaryQuestionStrategy implements QuestionStrategy {
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private static final String[] OPERATORS = {"+", "-", "*", "/"};
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private final Random random = new Random();
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@Override
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public String generateQuestion() {
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int operandsCount = random.nextInt(4) + 2; // 操作数数量：2~5
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StringBuilder sb = new StringBuilder();
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// 生成运算符序列
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String[] chosenOps = generateOperators(operandsCount);
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// 随机决定括号位置
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int[] parentheses = decideParentheses(operandsCount, chosenOps);
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// 拼接表达式
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buildExpression(sb, operandsCount, chosenOps, parentheses);
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return sb.toString();
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}
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/**
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* 根据操作数数量，随机生成运算符数组。
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*
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* @param operandsCount 操作数数量
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* @return 随机生成的运算符数组，长度为操作数数量 - 1
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*/
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private String[] generateOperators(int operandsCount) {
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String[] chosenOps = new String[operandsCount - 1];
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for (int i = 0; i < operandsCount - 1; i++) {
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chosenOps[i] = OPERATORS[random.nextInt(OPERATORS.length)];
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private final Random random = new Random();
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private final String[] operators = {"+", "-", "*", "/"};
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@Override
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public String generateQuestion() {
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int operandsCount = random.nextInt(4) + 2; // 操作数 2~5
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StringBuilder sb = new StringBuilder();
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// 生成运算符序列
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String[] chosenOps = generateOperators(operandsCount);
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// 随机决定括号
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int[] parentheses = decideParentheses(operandsCount, chosenOps);
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// 拼接表达式
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buildExpression(sb, operandsCount, chosenOps, parentheses);
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return sb.toString();
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}
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/**
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* 生成运算符序列
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* 根据操作数数量，随机生成对应数量的运算符数组
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*
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* @param operandsCount 操作数数量
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* @return 随机生成的运算符数组，长度为操作数数量-1
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*/
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private String[] generateOperators(int operandsCount) {
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String[] chosenOps = new String[operandsCount - 1];
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for (int i = 0; i < operandsCount - 1; i++) {
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chosenOps[i] = operators[random.nextInt(operators.length)];
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}
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return chosenOps;
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}
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/**
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* 决定是否需要括号，并返回括号的起始和结束位置
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* 对于3个及以上操作数，随机决定是否添加括号，并检查括号是否有效
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*
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* @param operandsCount 操作数数量
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* @param chosenOps 运算符数组
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* @return 包含开括号和闭括号位置的数组，格式为[openParenIndex, closeParenIndex]，-1表示不添加括号
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*/
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private int[] decideParentheses(int operandsCount, String[] chosenOps) {
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int openParenIndex = -1;
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int closeParenIndex = -1;
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if (operandsCount > 2 && random.nextBoolean()) {
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openParenIndex = random.nextInt(operandsCount - 1);
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closeParenIndex = random.nextInt(operandsCount - openParenIndex - 1) + openParenIndex + 1;
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// 如果括号包裹整个表达式，则不需要括号
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if (openParenIndex == 0 && closeParenIndex == operandsCount - 1) {
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openParenIndex = -1;
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closeParenIndex = -1;
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} else {
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// 检查括号内的运算符优先级是否相同，如果相同则不需要括号
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boolean samePrecedence = checkPrecedenceEquality(chosenOps, openParenIndex, closeParenIndex);
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if (samePrecedence) {
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openParenIndex = -1;
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closeParenIndex = -1;
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}
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}
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}
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return new int[]{openParenIndex, closeParenIndex};
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}
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/**
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* 判断括号内的运算符优先级是否相同
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* 用于决定是否需要添加括号（如果优先级都相同，则括号是冗余的）
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*
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* @param chosenOps 运算符数组
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* @param openParenIndex 开括号位置
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* @param closeParenIndex 闭括号位置
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* @return 如果括号内所有运算符优先级相同则返回true，否则返回false
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*/
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private boolean checkPrecedenceEquality(String[] chosenOps, int openParenIndex, int closeParenIndex) {
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int precedence = getPrecedence(chosenOps[openParenIndex]);
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for (int i = openParenIndex; i < closeParenIndex; i++) {
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if (getPrecedence(chosenOps[i]) != precedence) {
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return false;
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}
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}
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return true;
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}
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/**
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* 构建数学表达式
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* 根据操作数、运算符和括号位置，拼接完整的数学表达式
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*
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* @param sb StringBuilder对象，用于构建表达式
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* @param operandsCount 操作数数量
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* @param chosenOps 运算符数组
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* @param parentheses 括号位置数组，格式为[openParenIndex, closeParenIndex]
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*/
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private void buildExpression(StringBuilder sb, int operandsCount, String[] chosenOps, int[] parentheses) {
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int prevNum = random.nextInt(100) + 1;
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int openParenIndex = parentheses[0];
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int closeParenIndex = parentheses[1];
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// 处理第一个操作数可能的开括号
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if (openParenIndex == 0) sb.append("(");
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sb.append(prevNum);
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// 处理最后一个操作数可能的闭括号
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if (closeParenIndex == operandsCount - 1) sb.append(")");
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// 构建剩余的操作数和运算符
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for (int i = 1; i < operandsCount; i++) {
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String op = chosenOps[i - 1];
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sb.append(" ").append(op).append(" ");
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// 根据运算符生成下一个操作数
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int num = generateOperand(op, prevNum);
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// 添加括号（如果需要）
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if (i == openParenIndex) sb.append("(");
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sb.append(num);
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if (i == closeParenIndex) sb.append(")");
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prevNum = num; // 更新上一个数字，供下一轮计算使用
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}
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}
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/**
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* 生成每个操作数
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* 确保生成的操作数符合题目要求，特别是减法不会导致负数结果
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*
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* @param op 当前运算符
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* @param prevNum 前一个操作数的值
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* @return 生成的操作数
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*/
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private int generateOperand(String op, int prevNum) {
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int num = random.nextInt(100) + 1; // 默认生成1-100之间的随机数
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// 如果是减法运算符，确保不会出现负数结果
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if (op.equals("-") && num > prevNum) {
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num = random.nextInt(prevNum) + 1; // 保证 num <= prevNum，避免负数结果
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}
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return num;
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}
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private int getPrecedence(String op) {
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if (op.equals("+") || op.equals("-")) return 1;
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if (op.equals("*") || op.equals("/")) return 2;
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return 0;
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}
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return chosenOps;
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}
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/**
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* 构建数学表达式。
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*
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* @param sb StringBuilder 对象
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* @param operandsCount 操作数数量
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* @param chosenOps 运算符数组
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* @param parentheses 括号位置数组 [openParenIndex, closeParenIndex]
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*/
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private void buildExpression(
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StringBuilder sb, int operandsCount, String[] chosenOps, int[] parentheses) {
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int openParenIndex = parentheses[0];
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int closeParenIndex = parentheses[1];
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// 生成第一个操作数
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int prevNum = random.nextInt(100) + 1;
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// 如果开括号在第一个操作数之前
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if (openParenIndex == 0) {
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sb.append("(");
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}
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sb.append(prevNum);
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// 如果闭括号在第一个操作数之后（即只包含第一个操作数）
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if (closeParenIndex == 0) {
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sb.append(")");
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}
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for (int i = 1; i < operandsCount; i++) {
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String op = chosenOps[i - 1];
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sb.append(" ").append(op).append(" ");
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int num = generateOperand(op, prevNum);
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// 如果开括号在当前操作数之前
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if (i == openParenIndex) {
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sb.append("(");
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}
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sb.append(num);
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// 如果闭括号在当前操作数之后
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if (i == closeParenIndex) {
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sb.append(")");
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}
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prevNum = num;
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}
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// 确保括号正确闭合（安全措施）
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String expression = sb.toString();
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int openCount = countChar(expression, '(');
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int closeCount = countChar(expression, ')');
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// 如果括号不匹配，重新生成表达式
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if (openCount != closeCount) {
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sb.setLength(0); // 清空 StringBuilder
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// 递归调用生成新的表达式（或者去掉所有括号）
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buildExpressionWithoutParentheses(sb, operandsCount, chosenOps);
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}
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}
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/**
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* 构建没有括号的表达式（备用方法）。
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*/
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private void buildExpressionWithoutParentheses(
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StringBuilder sb, int operandsCount, String[] chosenOps) {
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int prevNum = random.nextInt(100) + 1;
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sb.append(prevNum);
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for (int i = 1; i < operandsCount; i++) {
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String op = chosenOps[i - 1];
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sb.append(" ").append(op).append(" ");
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int num = generateOperand(op, prevNum);
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sb.append(num);
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prevNum = num;
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}
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}
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/**
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* 计算字符串中特定字符的数量。
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*
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* @param str 输入字符串
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* @param ch 要统计的字符
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* @return 字符出现次数
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*/
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private int countChar(String str, char ch) {
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int count = 0;
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for (int i = 0; i < str.length(); i++) {
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if (str.charAt(i) == ch) {
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count++;
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}
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}
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return count;
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}
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/**
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* 决定是否需要括号，并返回括号位置。 改进版本：确保括号位置有效。
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*
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* @param operandsCount 操作数数量
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* @param chosenOps 运算符数组
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* @return 括号位置数组 [openParenIndex, closeParenIndex]
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*/
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private int[] decideParentheses(int operandsCount, String[] chosenOps) {
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if (operandsCount <= 2) {
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return new int[] {-1, -1}; // 操作数太少，不需要括号
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}
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if (!random.nextBoolean()) {
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return new int[] {-1, -1}; // 随机决定不加括号
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}
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// 生成有效的括号位置
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int openParenIndex = random.nextInt(operandsCount - 1);
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int closeParenIndex =
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random.nextInt(operandsCount - openParenIndex - 1) + openParenIndex + 1;
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// 确保至少包含 2 个操作数
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if (closeParenIndex - openParenIndex < 2) {
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closeParenIndex = openParenIndex + 1;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
// 如果括号包裹整个表达式，则不需要括号
|
|
|
|
|
if (openParenIndex == 0 && closeParenIndex == operandsCount - 1) {
|
|
|
|
|
return new int[] {-1, -1};
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
// 检查括号内运算符是否同一优先级，如果是则不需要括号
|
|
|
|
|
boolean samePrecedence = checkPrecedenceEquality(chosenOps, openParenIndex, closeParenIndex);
|
|
|
|
|
if (samePrecedence) {
|
|
|
|
|
return new int[] {-1, -1};
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
return new int[] {openParenIndex, closeParenIndex};
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/**
|
|
|
|
|
* 判断括号内的运算符是否具有相同优先级。
|
|
|
|
|
*
|
|
|
|
|
* @param chosenOps 运算符数组
|
|
|
|
|
* @param openParenIndex 开括号位置
|
|
|
|
|
* @param closeParenIndex 闭括号位置
|
|
|
|
|
* @return true 如果括号内运算符优先级相同
|
|
|
|
|
*/
|
|
|
|
|
private boolean checkPrecedenceEquality(
|
|
|
|
|
String[] chosenOps, int openParenIndex, int closeParenIndex) {
|
|
|
|
|
int precedence = getPrecedence(chosenOps[openParenIndex]);
|
|
|
|
|
for (int i = openParenIndex; i < closeParenIndex; i++) {
|
|
|
|
|
if (getPrecedence(chosenOps[i]) != precedence) {
|
|
|
|
|
return false;
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
return true;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/**
|
|
|
|
|
* 根据运算符生成操作数。
|
|
|
|
|
*
|
|
|
|
|
* <p>特别处理减法，确保不会出现负数结果。
|
|
|
|
|
*
|
|
|
|
|
* @param op 当前运算符
|
|
|
|
|
* @param prevNum 上一个操作数
|
|
|
|
|
* @return 生成的操作数
|
|
|
|
|
*/
|
|
|
|
|
private int generateOperand(String op, int prevNum) {
|
|
|
|
|
int num = random.nextInt(100) + 1;
|
|
|
|
|
if (op.equals("-") && num > prevNum) {
|
|
|
|
|
num = random.nextInt(prevNum) + 1;
|
|
|
|
|
}
|
|
|
|
|
return num;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/**
|
|
|
|
|
* 获取运算符的优先级。
|
|
|
|
|
*
|
|
|
|
|
* @param op 运算符
|
|
|
|
|
* @return 优先级数值
|
|
|
|
|
*/
|
|
|
|
|
private int getPrecedence(String op) {
|
|
|
|
|
if (op.equals("+") || op.equals("-")) {
|
|
|
|
|
return 1;
|
|
|
|
|
}
|
|
|
|
|
if (op.equals("*") || op.equals("/")) {
|
|
|
|
|
return 2;
|
|
|
|
|
}
|
|
|
|
|
return 0;
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
|
