写一个cpp代码，生成一棵哈夫曼树，并进行编码和解码操作

在C++中，我们可以使用优先队列（`std::priority_queue`）和一个简单的节点结构来创建哈夫曼树。首先，我们定义节点类（HuffmanNode），然后实现编码、解码以及构建哈夫曼树的函数。这里是一个简化的示例：

#include <queue>
#include <map>

// 定义节点类
struct HuffmanNode {
    char data;
    int freq;
    HuffmanNode* left = nullptr;
    HuffmanNode* right = nullptr;

    HuffmanNode(char ch, int f) : data(ch), freq(f) {}
};

// 比较节点频率的比较函数
bool compare(HuffmanNode* a, HuffmanNode* b) {
    return a->freq > b->freq;
}

// 构建哈夫曼树的函数
HuffmanNode* buildHuffmanTree(std::vector<HuffmanNode*>& nodes) {
    if (nodes.empty()) return nullptr;

    std::priority_queue<HuffmanNode*, std::vector<HuffmanNode*>, decltype(compare)> pq(compare);
    for (HuffmanNode* node : nodes)
        pq.push(node);

    while (pq.size() > 1) {
        HuffmanNode* left = pq.top(); pq.pop();
        HuffmanNode* right = pq.top(); pq.pop();
        HuffmanNode* newNode = new HuffmanNode('\0', left->freq + right->freq);
        newNode->left = left;
        newNode->right = right;
        pq.push(newNode);
    }
    return pq.top(); // 返回根节点
}

// 编码和解码函数
std::string encode(const HuffmanNode* root, const char& input) {
    std::string code;
    HuffmanNode* current = root;
    while (input != '\0') {
        if (input == current->data) {
            code += '1';
            current = current->left;
        } else {
            code += '0';
            current = current->right;
        }
        input--;
    }
    return code;
}

std::string decode(const HuffmanNode* root, const std::string& code) {
    std::string result = "";
    HuffmanNode* current = root;
    for (char bit : code) {
        if (bit == '1')
            current = current->left;
        else
            current = current->right;
        if (!current->left && !current->right) { // 如果遇到叶子节点，结束解码
            result += current->data;
            current = root; // 重新设置当前节点到根节点，准备下一个字符
        }
    }
    return result;
}

int main() {
    std::vector<HuffmanNode*> nodes = {/* 初始化一些有频率的字符节点 */ ...};
    HuffmanNode* huffmanRoot = buildHuffmanTree(nodes);

    // 示例编码和解码
    std::string encodedCode = encode(huffmanRoot, 'a'); // 用字符'a'进行编码
    std::string decodedString = decode(huffmanRoot, encodedCode); // 解码编码后的字符串

    std::cout << "Encoded Code: " << encodedCode << std::endl;
    std::cout << "Decoded String: " << decodedString << std::endl;

    delete huffmanRoot; // 清理内存
    return 0;
}