用C++给出哈夫曼编码程序的实现代码，以及测试数据

下面是一个简单的 C++ 实现哈夫曼编码的代码：

#include <iostream>
#include <queue>
#include <unordered_map>
#include <vector>
using namespace std;

struct Node {
    char ch;
    int freq;
    Node* left;
    Node* right;
    Node(char c, int f) : ch(c), freq(f), left(nullptr), right(nullptr) {}
};

struct Compare {
    bool operator()(Node* a, Node* b) {
        return a->freq > b->freq;
    }
};

void getHuffmanCodes(Node* root, string code, unordered_map<char, string>& huffmanCodes) {
    if (root == nullptr) {
        return;
    }
    if (root->left == nullptr && root->right == nullptr) {
        huffmanCodes[root->ch] = code;
    }
    getHuffmanCodes(root->left, code + "0", huffmanCodes);
    getHuffmanCodes(root->right, code + "1", huffmanCodes);
}

vector<pair<char, int>> getFrequencies(string s) {
    unordered_map<char, int> freq;
    for (char c : s) {
        freq[c]++;
    }
    vector<pair<char, int>> freqList(freq.begin(), freq.end());
    return freqList;
}

Node* buildHuffmanTree(vector<pair<char, int>>& freqList) {
    priority_queue<Node*, vector<Node*>, Compare> pq;
    for (auto& p : freqList) {
        Node* node = new Node(p.first, p.second);
        pq.push(node);
    }
    while (pq.size() > 1) {
        Node* left = pq.top();
        pq.pop();
        Node* right = pq.top();
        pq.pop();
        Node* node = new Node('$', left->freq + right->freq);
        node->left = left;
        node->right = right;
        pq.push(node);
    }
    return pq.top();
}

string encode(string s) {
    unordered_map<char, string> huffmanCodes;
    vector<pair<char, int>> freqList = getFrequencies(s);
    Node* root = buildHuffmanTree(freqList);
    getHuffmanCodes(root, "", huffmanCodes);
    string encodedString = "";
    for (char c : s) {
        encodedString += huffmanCodes[c];
    }
    return encodedString;
}

int main() {
    string s = "hello world";
    string encodedString = encode(s);
    cout << "Original string: " << s << endl;
    cout << "Encoded string: " << encodedString << endl;
    return 0;
}

测试数据：

hello world