【贪心算法】哈夫曼编码

哈夫曼编码

 以下是哈夫曼编码的简陋实现方式，使用了STL库中的Vector和优先队列。只能对单字符进行编码，无法对中文进行编码，且算法有待改进。

 

  1 #include <iostream>
  2 #include <string>
  3 #include <vector>
  4 #include <queue>
  5 using namespace std;
  6 //哈夫曼树节点类
  7 class HuffmanNode 
  8 {
  9 public:
 10     int weight=0;       //权值
 11     char ch;            //节点值
 12     HuffmanNode* left;  //左孩子
 13     HuffmanNode* right; //右孩子
 14     HuffmanNode* parent;// 父结点
 15     string code = "";
 16     HuffmanNode(double w, char c=NULL, HuffmanNode* l=NULL, HuffmanNode* r=NULL, HuffmanNode* p=NULL) :
 17         weight(w), ch(c), left(l), right(r), parent(p) {}
 18 };
 19 //STL库优先队列小顶堆比较类
 20 class cmp
 21 {
 22 public:
 23     bool operator () (HuffmanNode*& a, HuffmanNode*& b) const
 24     {
 25         return a->weight > b->weight;
 26     }
 27 };
 28 //前序遍历编码
 29 void postOrderCoding(HuffmanNode* root,string code="")
 30 {
 31     if (root != NULL)
 32     {
 33         postOrderCoding(root->left,code+'0');
 34         postOrderCoding(root->right,code+'1');
 35         root->code = code;
 36     }
 37 }
 38 //释放内存
 39 void destroyTree(HuffmanNode* root)
 40 {
 41     if (root != NULL)
 42     {
 43         destroyTree(root->left);
 44         destroyTree(root->right);
 45         delete root;
 46     }
 47 }
 48 //构建哈夫曼树
 49 vector<HuffmanNode*> createHuffmanTree(string str)
 50 {
 51     //处理字符串，得到叶节点以及叶节点对应的权重
 52     vector<HuffmanNode*> nodes;//（vector）nodes存放叶节点
 53     for (int i = 0; i < str.size(); i++)
 54     {
 55         bool flag = false;
 56         for (int j = 0; j < nodes.size(); j++)
 57         {
 58             if (str[i] == nodes[j]->ch)
 59             {
 60                 flag = true;
 61                 nodes[j]->weight++;
 62                 break;
 63             }
 64         }
 65         if (!flag)
 66             nodes.push_back(new HuffmanNode(1, str[i]));
 67     }
 68     //简单地使用STL库中的优先队列
 69     priority_queue<HuffmanNode* ,vector<HuffmanNode*>,cmp> q;
 70     for (int i = 0; i < nodes.size(); i++)
 71         q.push(nodes[i]);
 72     //选择队列中权重最小的两棵树合并，将合并后的树放入优先队列中
 73     while (q.size() != 1)
 74     {
 75         HuffmanNode* temp1 = q.top();
 76         q.pop();
 77         HuffmanNode* temp2 = q.top();
 78         q.pop();
 79         if (temp1->weight > temp2->weight)
 80             swap(temp1, temp2);
 81         HuffmanNode* father = new HuffmanNode(temp1->weight + temp2->weight, NULL, temp1, temp2);
 82         q.push(father);
 83     }
 84     //nodes首位存放哈夫曼树根节点
 85     nodes.insert(nodes.begin(), q.top());
 86     //进行编码
 87     postOrderCoding(q.top());
 88     return nodes;
 89 }
 90 int main()
 91 {
 92     string str;
 93     for (;;)
 94     {
 95         getline(cin, str);
 96         vector<HuffmanNode*> nodes;
 97         nodes = createHuffmanTree(str);
 98         for (int i = 1; i < nodes.size(); i++)
 99         {
100             cout << nodes[i]->ch << ":" << nodes[i]->code << endl;
101         }
102         destroyTree(nodes[0]);
103     }
104 }

 

 

 

 

posted @ 2020-05-15 14:37  吃土poQAQ  阅读(463)  评论(0)  编辑  收藏  举报