哈夫曼编码和译码代码

哈夫曼编码是一种基于字符出现频率进行编码的算法，其主要思想是将出现频率高的字符用较短的编码表示，而出现频率低的字符则用较长的编码表示。这样可以有效地减少编码长度，从而达到压缩数据的目的。下面是一个简单的哈夫曼编码和译码的代码实现：

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

// 哈夫曼树节点
struct Node {
    char ch;  // 字符
    int freq; // 频率
    Node* left;
    Node* right;
    Node(char c, int f) : ch(c), freq(f), left(nullptr), right(nullptr) {}
};

// 比较函数
struct cmp {
    bool operator() (Node* a, Node* b) {
        return a->freq > b->freq;
    }
};

// 构建哈夫曼树
Node* buildHuffmanTree(const string& s) {
    unordered_map<char, int> freqMap;
    for (char c : s) {
        freqMap[c]++;
    }

    priority_queue<Node*, vector<Node*>, cmp> pq;
    for (auto it = freqMap.begin(); it != freqMap.end(); it++) {
        pq.push(new Node(it->first, it->second));
    }

    while (pq.size() > 1) {
        Node* left = pq.top(); pq.pop();
        Node* right = pq.top(); pq.pop();
        Node* parent = new Node('$', left->freq + right->freq);
        parent->left = left;
        parent->right = right;
        pq.push(parent);
    }

    return pq.top();
}

// 生成哈夫曼编码表
void generateHuffmanCodes(Node* root, string code, unordered_map<char, string>& codes) {
    if (!root) return;

    if (root->ch != '$') {
        codes[root->ch] = code;
    }

    generateHuffmanCodes(root->left, code + "0", codes);
    generateHuffmanCodes(root->right, code + "1", codes);
}

// 哈夫曼编码
string encode(const string& s) {
    Node* root = buildHuffmanTree(s);
    unordered_map<char, string> codes;
    generateHuffmanCodes(root, "", codes);

    string res = "";
    for (char c : s) {
        res += codes[c];
    }

    return res;
}

// 哈夫曼译码
string decode(Node* root, const string& code) {
    string res = "";
    Node* cur = root;
    for (char c : code) {
        if (c == '0') {
            cur = cur->left;
        } else {
            cur = cur->right;
        }

        if (cur->ch != '$') {
            res += cur->ch;
            cur = root;
        }
    }

    return res;
}

int main() {
    string s = "hello world";
    string encoded = encode(s);
    cout << "Encoded: " << encoded << endl;

    Node* root = buildHuffmanTree(s);
    string decoded = decode(root, encoded);
    cout << "Decoded: " << decoded << endl;

    return 0;
}