Data-Structure/Exercise/Homework3/grok的表达式树模板.cpp

#include <iostream>
#include <memory>
#include <string>
#include <vector>

enum class NodeType {
    OPERAND,  // 操作数
    OPERATOR  // 运算符
};

class ExprNode {
public:
    NodeType node_type;
    std::unique_ptr<ExprNode> left;
    std::unique_ptr<ExprNode> right;

    virtual ~ExprNode() = default;
    virtual std::string toString() const = 0;
};

class OperandNode : public ExprNode {
public:
    int value;

    OperandNode(int val) : value(val) {
        node_type = NodeType::OPERAND;
    }

    std::string toString() const override {
        return "Operand(" + std::to_string(value) + ")";
    }
};

class OperatorNode : public ExprNode {
public:
    std::string op;

    OperatorNode(const std::string& oper, std::unique_ptr<ExprNode> l = nullptr, std::unique_ptr<ExprNode> r = nullptr)
        : op(oper) {
        node_type = NodeType::OPERATOR;
        left = std::move(l);
        right = std::move(r);
    }

    std::string toString() const override {
        std::string left_str = left ? " " + left->toString() : "";
        std::string right_str = right ? " " + right->toString() : "";
        return "Operator(" + op + left_str + right_str + ")";
    }
};

class ExprTree {
private:
    std::unique_ptr<ExprNode> root;

public:
    ExprTree(std::unique_ptr<ExprNode> r = nullptr) : root(std::move(r)) {}

    void setRoot(std::unique_ptr<ExprNode> r) {
        root = std::move(r);
    }

    // 示例：中序遍历（Inorder Traversal），用于打印表达式
    void inorderTraversal(const std::unique_ptr<ExprNode>& node, std::vector<std::string>& result) const {
        if (!node) return;
        inorderTraversal(node->left, result);
        if (node->node_type == NodeType::OPERAND) {
            auto operand = static_cast<const OperandNode*>(node.get());
            result.push_back(std::to_string(operand->value));
        } else {
            auto oper = static_cast<const OperatorNode*>(node.get());
            result.push_back(oper->op);
        }
        inorderTraversal(node->right, result);
    }

    std::string toInfixString() const {
        std::vector<std::string> result;
        inorderTraversal(root, result);
        if (result.empty()) return "";
        // 简化输出：实际中需处理括号以正确表示优先级
        std::string infix;
        for (const auto& s : result) {
            infix += s + " ";
        }
        return infix.substr(0, infix.size() - 1);  // 移除末尾空格
    }

    // 示例：从简单中缀表达式构建树（简化版，仅支持基本 + - * / 和括号）
    // 注意：这是一个简化实现，使用递归下降解析器。你可以扩展它。
    static std::unique_ptr<ExprNode> buildFromInfix(const std::string& expr, size_t& pos) {
        // 跳过空格
        while (pos < expr.size() && expr[pos] == ' ') ++pos;

        if (pos >= expr.size()) return nullptr;

        char ch = expr[pos];
        if (isdigit(ch)) {
            // 解析数字
            int num = 0;
            while (pos < expr.size() && isdigit(expr[pos])) {
                num = num * 10 + (expr[pos++] - '0');
            }
            return std::make_unique<OperandNode>(num);
        } else if (ch == '(') {
            ++pos;  // 跳过 '('
            auto left = buildFromInfix(expr, pos);
            auto op_node_raw = buildFromInfix(expr, pos);  // 运算符
            auto right = buildFromInfix(expr, pos);
            if (pos < expr.size() && expr[pos] == ')') ++pos;
            if (op_node_raw && op_node_raw->node_type == NodeType::OPERATOR) {
                auto op_node = std::unique_ptr<OperatorNode>(static_cast<OperatorNode*>(op_node_raw.release()));
                op_node->left = std::move(left);
                op_node->right = std::move(right);
                return std::move(op_node);
            }
            return nullptr;  // 错误
        } else if (ch == '+' || ch == '-' || ch == '*' || ch == '/') {
            std::string oper(1, expr[pos++]);
            return std::make_unique<OperatorNode>(oper);
        }
        return nullptr;
    }

    // 便捷方法：从字符串构建树
    void buildFromInfix(const std::string& expr) {
        size_t pos = 0;
        root = buildFromInfix(expr, pos);
    }
};

// 示例使用
int main() {
    // 手动构建树：3 + (4 * 5)
    auto mul = std::make_unique<OperatorNode>("*");
    mul->left = std::make_unique<OperandNode>(4);
    mul->right = std::make_unique<OperandNode>(5);

    auto add = std::make_unique<OperatorNode>("+");
    add->left = std::make_unique<OperandNode>(3);
    add->right = std::move(mul);

    ExprTree tree(std::move(add));
    std::cout << "树表示: " << tree.root->toString() << std::endl;
    std::cout << "中序: " << tree.toInfixString() << std::endl;  // 输出如 "3 + * 4 5"

    // 从字符串构建（简化，仅基本支持）
    ExprTree tree2;
    tree2.buildFromInfix("3+(4*5)");  // 需要完善解析器以处理完整表达式
    std::cout << "从字符串构建: " << (tree2.root ? tree2.root->toString() : "无效") << std::endl;

    return 0;
}