霍夫曼编码（Huffman Code） 简单模拟

Posted 2020-10-14

这周的数据结构实验作业，刚好被抽到号要上交，于是乎在宿舍写了一晚上。

若有错漏之处请斧正！

关于建树的参考博文：http://blog.csdn.net/xgf415/article/details/52628073

 

实验要求如下：

---

---

 

编译器：VS 2015

运行环境： WIN 10

 

代码如下：

hfmTree.h

  1 #include <string>
  2 #include "MinHeap.h"
  3 #include <stack>
  4 #include <sstream>
  5 using namespace std;
  6 #pragma once
  7 
  8 
  9 const char EndTag = ‘#‘; //读写文件标识用，用来标记NULL孩子指针
 10 const char NoneTag = ‘*‘; //建树识别用，非字符结点
 11 class HuffmanTree; //前置声明
 12 class Node
 13 {
 14 private:
 15     char ch;
 16     float wei;
 17     string code;
 18     Node *lc, *rc;
 19 
 20     friend class HuffmanTree;
 21 public :
 22     Node() : ch(NoneTag),wei(0),code(),lc(NULL),rc(NULL){}
 23     Node(char c, float w) {
 24         ch = c;
 25         wei= w;
 26         lc = NULL;
 27         rc = NULL;
 28     }
 29 
 30     float getWeight() { return wei; }
 31     char getChar() { return ch; }
 32     string getCode() { return code; }
 33     Node* getRightChild() const { return rc; }
 34     Node* getLeftChild() const { return lc; }
 35     void setCodes(const string &s) { code = s; }
 36     void set(const Node& l, const Node & r) { lc = new Node(l); rc = new Node(r); }
 37     void clone(Node &n) {
 38         ch = n.getChar(); 
 39         wei = n.getWeight(); 
 40         code = n.getCode(); 
 41         lc = n.getLeftChild(); 
 42         rc = n.getRightChild();
 43     }
 44 
 45     bool hasChild()
 46     {
 47         return rc != NULL && lc != NULL;
 48     }
 49 
 50     Node &operator = (const Node &n) {
 51         ch = n.ch;
 52         wei = n.wei;
 53         code = n.code;
 54         lc = n.lc;
 55         rc = n.rc;
 56         return *this;
 57     }
 58 
 59     bool operator <=(Node &R) {
 60         return wei <= R.wei;
 61     }
 62 
 63     bool operator >(Node &R) {
 64         return wei > R.wei;
 65     }
 66 
 67     bool operator < (Node &R) {
 68         return wei < R.wei;
 69     }
 70 
 71     friend ostream & operator << (ostream &out, const Node& n) {
 72         out << "Char:" << n.ch << ‘\\t‘ << "Weight:" << n.wei << endl;
 73         return out;
 74     }
 75 
 76 };
 77 
 78 class HuffmanTree
 79 {
 80 private:
 81     int size; //结点数，包括空格结点
 82     Node *root;
 83     bool has_EndTag;
 84 
 85     float averageLen;
 86 public:
 87     HuffmanTree() {
 88         size = 0;
 89         has_EndTag = false;
 90         root = NULL;
 91     }
 92 
 93     //建立哈夫曼树
 94     HuffmanTree(MinHeap<Node> &mh)
 95     {
 96         has_EndTag = false;
 97         Node first, second;
 98         while (mh.getSize() != 1)
 99         {
100             mh.RemoveMin(first);
101             mh.RemoveMin(second);
102             Node h(NoneTag, first.getWeight() + second.getWeight());
103             h.set(first, second);
104             mh.Insert(h);
105         }
106         mh.RemoveMin(first);
107         root = new Node(first);
108     }
109 
110     void BuildTree(MinHeap<Node> &mh)
111     {
112         if (root != NULL)    DeleteTree(root);
113         has_EndTag = false;
114         Node first, second;
115         while (mh.getSize() != 1)
116         {
117             mh.RemoveMin(first);
118             mh.RemoveMin(second);
119             Node h(NoneTag, first.getWeight() + second.getWeight());
120             h.set(first, second);
121             mh.Insert(h);
122         }
123         mh.RemoveMin(first);
124         root = new Node(first);
125     }
126 
127     void DeleteTree(Node *t) //删除以t为根的子树
128     {
129         if (t == NULL)
130             return;
131         else 
132         {
133             Node *p1 = t->lc;
134             Node *p2 = t->rc;
135             if (p1 != NULL)        DeleteTree(p1);
136             if (p2 != NULL)        DeleteTree(p2);
137             delete t;
138         }
139     }
140     void Initialize()
141     {
142         string s = "";
143         Initialization(root, s);
144     }
145     
146     void Initialization(Node *n,string s)        //初始化编码表
147     {
148         if (n == NULL)        return;
149         n->code = s;
150         Initialization(n->lc, s + ‘0‘);
151         Initialization(n->rc, s + ‘1‘);
152     }
153 
154     void addTag(Node *p) //添加结尾标志的递归函数（方便读写文件）
155     {
156         if (p->lc == NULL)
157         {
158             Node *t = new Node(EndTag, 0);
159             p->lc = t;
160         }
161         else addTag(p->lc);
162         if (p->rc == NULL)
163         {
164             Node *t = new Node(EndTag, 0);
165             p->rc = t;
166         }
167         else addTag(p->rc);
168     }
169 
170     void  addLeafTag() //给Huffman树添加叶子结点的空子女标志结点#，方便文件读写
171     {
172         addTag(root);
173         has_EndTag = true;
174     }
175 
176     void delTag(Node *p)  //删除叶子结点的空子女标志结点的递归函数
177     {
178         if (p == NULL)
179             return;
180         if (p->ch == EndTag)
181             delete p;
182         if (p->rc != NULL)
183             delTag(p->rc);
184         if (p->lc != NULL)
185             delTag(p->lc);
186     }
187 
188     void delLeafTag()      //删除叶子结点的空子女标志结点
189     {
190         delTag(root);
191         has_EndTag = false;
192     }
193 
194     void SaveTable(ostream &os) //储存编码表到文件(非递归前序遍历)
195     {
196 
197         if (!has_EndTag)
198             addLeafTag();
199         stack<Node *> S;
200         Node *p = root;
201         S.push(p);
202         while (!S.empty())
203         {
204             p = S.top();        S.pop();
205             Node temp = *p;
206             os << temp.ch << ‘ ‘ << temp.wei <<‘ ‘ << temp.code << endl;
207             if (p->lc != NULL)        S.push(p->lc);
208             if (p->rc != NULL)        S.push(p->rc);
209         }
210     }
211 
212     void ReadTable(istream &is) //读取编码表
213     {
214         if (root != NULL)        DeleteTree(root);
215         ReadTable(is, root);
216         if (root == NULL)
217             cout << "error !读取文件遇到问题！" << endl;
218     }
219 
220     void ReadTable(istream &is, Node *&dest) //读取编码表的递归函数
221     {
222         if (!is.eof())
223         {
224             string line;
225             getline(is, line);
226             Node temp;
227             stringstream ss(line);
228             if (line[0] == ‘ ‘)
229             {
230                 temp.ch = ‘ ‘;
231                 ss >> temp.wei >> temp.code;
232             }
233             else
234                 ss >> temp.ch >> temp.wei >> temp.code;
235             if (temp.ch == EndTag)
236             {
237                 dest = NULL;
238                 return;
239             }
240             dest = new Node(temp);
241             ReadTable(is, dest->lc);
242             ReadTable(is, dest->rc);
243         }
244     }
245 
246     void ShowTree()
247     {
248         Show(root);
249         averageLen = averageLen / size;
250         cout << "平均编码长度：" << averageLen << endl;
251     }
252 
253     void Show(Node *n) //前序遍历输出编码结果
254     {
255         if (n == NULL)    return;
256         if (n->ch != NoneTag)
257         {
258             cout << n->ch << "：";
259             cout <<n->code << endl;
260             averageLen += n->code.length();
261             size++;
262         }
263         Show(n->lc);
264         Show(n->rc);
265     }
266 
267     string getCode(char c) //给字符c编码，返回c的编码
268     {
269         Node *p = SearchChar(root,c);
270         if (p == NULL)
271         {
272             cout << "找不到" << c << "对应的编码" << endl;
273             exit(1);
274         }
275         else
276             return p->code;
277     }
278 
279     Node *SearchChar(Node *p,char c)  //查找字符为c的结点递归函数
280     {
281         if (p->ch == c)
282             return p;
283         else
284         {
285             Node *cur = NULL;
286             if (p->rc != NULL)
287             {
288                 Node *rc = SearchChar(p->rc, c);
289                 if (rc != NULL)        cur = rc;
290             }
291             if (p->lc != NULL)
292             {
293                 Node *lc = SearchChar(p->lc, c);
294                 if (lc != NULL)        cur = lc;
295             }
296             return cur;
297         }
298     }
299 
300     char getChar(string c)  //解码，返回编码c对应的字符
301     {
302         Node *p = SearchCode(root, c);
303         if (p == NULL) { cout << "解码失败，该字符不存在" << endl; return NoneTag; }
304         else    return p->ch;
305     }
306 
307     Node *SearchCode(Node *p, string c) //查找编码为c的对应字符结点
308     {
309         if (p->code == c)
310             return p;
311         else
312         {
313             Node *cur = NULL;
314             if (p->rc != NULL)
315             {
316                 Node *rc = SearchCode(p->rc, c);
317                 if (rc != NULL)        cur = rc;
318             }
319             if (p->lc != NULL)
320             {
321                 Node *lc = SearchCode(p->lc, c);
322                 if (lc != NULL)        cur = lc;
323             }
324             return cur;
325         }
326     }
327 };

 

建树要用到优先级队列，用最小堆模板类实现，代码如下：

MinHeap.h

  1 #pragma once
  2 #define DefaultSize 10
  3 template<class E>
  4 class MinHeap
  5 {
  6 private:
  7     E *heap;
  8     int currentSize;
  9     int maxHeapSize;
 10     void siftDown(int start, int m);
 11     void siftUp(int start);
 12 public:
 13     MinHeap(int sz = DefaultSize);
 14     MinHeap(E arr[], int n);
 15     ~MinHeap() { delete[]heap; }
 16     bool Insert(const E &x);
 17     bool RemoveMin(E &x);
 18     bool IsEmpty()const
 19     {return (currentSize == 0) ? true : false;}
 20     bool IsFull() const{return (currentSize == maxHeapSize) ? true : false;}
 21     void MakeEmpty() { currentSize = 0; }
 22 
 23     int getSize() const { return currentSize; }
 24     void showAll() {
 25         for (int i = 0; i < currentSize; ++i)
 26             cout << heap[i];
 27     }
 28 };
 29 
 30 template<class E>
 31 MinHeap<E>::MinHeap(int sz)
 32 {
 33     maxHeapSize = (DefaultSize < sz) ? sz : DefaultSize;
 34     heap = new E[maxHeapSize];
 35     if (heap == NULL) {
 36         exit(1);
 37     }
 38     currentSize = 0;
 39 }
 40 
 41 template<class E>
 42 MinHeap<E>::MinHeap(E arr[], int n)
 43 {
 44     maxHeapSize = (DefaultSize < n) ? n : DefaultSize;
 45     heap = new E[maxHeapSize];
 46     if (heap == NULL) {
 47         exit(1);
 48     }
 49     for (int i = 0; i < n; ++i)    heap[i] = arr[i];
 50     currentSize = n;
 51     int currentPos = (currentSize - 2) / 2;
 52     while (currentPos >= 0)
 53     {
 54         siftDown(currentPos, currentSize - 1);
 55         currentPos--;
 56     }
 57 }
 58 
 59 template<class E>
 60 void MinHeap<E>::siftDown(int start, int m)
 61 {
 62     if(m <= start)     return;
 63     int i = start, j = 2 * i + 1;
 64     E temp = heap[i];
 65     while (j <= m)
 66     {
 67         if (j < m && heap[j] > heap[j + 1]) j++;
 68         if (temp <= heap[j]) break;
 69         else { heap[i] = heap[j]; i = j; j = 2 * j + 1; }
 70     }
 71     heap[i] = temp;
 72 }
 73 
 74 template<class E>
 75 void MinHeap<E>::siftUp(int start)
 76 {
 77     int j = start, i = (j - 1) / 2; // i : parent, j : current
 78     E temp = heap[j];
 79     while (j > 0)
 80     {
 81         if (heap[i] <= temp)        break;     // parent is smaller    
 82         else { 
 83             heap[j] = heap[i];
 84             j = i; 
 85             i = (i - 1) / 2; 
 86         }
 87     }
 88     heap[j] = temp;
 89 }
 90 
 91 template<class E>
 92 bool MinHeap<E>::Insert(const E& x)
 93 {
 94     if (currentSize == maxHeapSize)
 95     {
 96         exit(1);
 97     }
 98     heap[currentSize] = x;
 99     siftUp(currentSize);
100     currentSize++;
101     return true;
102 }
103 
104 template<class E>
105 bool MinHeap<E>::RemoveMin(E &x)
106 {
107     if (currentSize == 0) {
108         std::cout << "Heap empty!" << std::endl;
109         std::cout << currentSize << endl;
110         return false;
111     }
112     else
113     {
114         x = heap[0];
115         heap[0] = heap[currentSize - 1];
116         currentSize--;
117         siftDown(0, currentSize - 1);
118         return true;
119     }
120     
121 }

 

下面是main.cpp

  1 #include <iostream>
  2 #include <fstream>
  3 #include "hfmTree.h"
  4 #define MaxCh 50
  5 using namespace std;
  6 const char * TreeFile = "hfmTree.txt";
  7 const char * ToBeTran = "ToBeTran.txt";
  8 const char * CodeFile = "CodeFile.txt";
  9 const char * TextFile = "TextFile.txt";
 10 
 11 void showMenu()
 12 {
 13     cout << "\\t\\tI：初始化（Initialization）" << endl;
 14     cout << "\\t\\tE：编码（Encoding）" << endl;
 15     cout << "\\t\\tD：译码（Decoding）" << endl;
 16     cout << "\\t\\tW: 重新写入正文" << endl;
 17     cout << "\\t\\tQ：退出" << endl;
 18     cout << endl;
 19 }
 20 
 21 void eatLine()
 22 {
 23     string line;
 24     getline(cin,line);
 25 }
 26 
 27 HuffmanTree hfmTree;
 28 bool has_init = false;
 29 void Initialization()
 30 {
 31     MinHeap<Node> mh(MaxCh);
 32     int n;
 33     cout << "请输入字符集中字符个数：";
 34     cin >> n;
 35     eatLine();
 36     while (n--)
 37     {
 38         char ch;
 39         float wei;
 40         cout << "输入编码字符：";
 41         ch = getchar();
 42         eatLine();
 43         cout << "输入权值：";
 44         cin >> wei;
 45         eatLine();
 46         Node t(ch, wei);
 47         mh.Insert(t);
 48         cout << t;
 49     }
 50     hfmTree.BuildTree(mh);
 51     hfmTree.Initialize();
 52     cout << "初始化编码表结果：" << endl;
 53     hfmTree.ShowTree();
 54     ofstream fout(TreeFile);
 55     hfmTree.SaveTable(fout);
 56     cout << "写入文件成功！" << endl;
 57     has_init = true;
 58     fout.close();
 59 }
 60 
 61 void ReadTreeFile()
 62 {
 63     ifstream fin(TreeFile, ios::app);
 64     hfmTree.ReadTable(fin);
 65     hfmTree.ShowTree();
 66     fin.close();
 67     has_init = true;
 68 }
 69 
 70 void WriteText()
 71 {
 72     ofstream fout(ToBeTran);
 73     if (!fout.is_open())
 74     {
 75         cout << "打开文件" << ToBeTran << "失败" << endl;
 76         return;
 77     }
 78     string text;
 79     eatLine();
 80     cout << "请输入需要编码的文本：" << endl;
 81     getline(cin, text);
 82     fout << text;
 83     cout << "写入原始文本成功！" << endl;
 84     fout.close();
 85 }
 86 
 87 void Encoding()
 88 {
 89     if (has_init == false)
 90         ReadTreeFile();
 91 
 92     ifstream fin(ToBeTran);
 93     if (!fin.is_open())
 94     {
 95         cout << "打开文件" << ToBeTran << "失败" << endl;
 96         return;
 97     }
 98 
 99     string text;
100     getline(fin, text);
101     cout << "将要给下述文本编码:" << endl;
102     cout << text << endl;
103     
104     int len = text.length();
105     cout << "length:" << len << endl;
106 
107     string code;
108     for (int i = 0; i < len; ++i)
109     {
110         string c = hfmTree.getCode(text[i]);
111         code += c;
112     }
113     cout << "编码结果为：" << endl;
114     cout << code << endl;
115     ofstream fout(CodeFile);
116     if (!fout.is_open())
117     {
118         cout << "打开文件" << CodeFile << "失败" << endl;
119         return;
120     }
121     fout << code;
122     cout << "编码成功！" << endl;
123     fout.close();
124     fin.close();
125 }
126 
127 void Decoding()
128 {
129     if (has_init == false)
130         ReadTreeFile();
131     ifstream fin(CodeFile);
132     if (!fin.is_open())
133     {
134         cout << "打开文件" << ToBeTran << "失败" << endl;
135         return;
136     }
137     string code;
138     fin >> code;
139     cout << "将要给下述编码进行解码:" << endl;
140     cout << code << endl;
141     string text;
142     int len = code.length();
143     string codenow;
144     for (int i = 0; i < len; ++i)
145     {
146         codenow += code[i];
147         char temp = hfmTree.getChar(codenow);
148         if (temp != NoneTag) { text += temp; codenow.clear(); }
149     }
150     cout << "解码结果为：" << endl;
151     cout << text <<endl;
152     ofstream fout(TextFile);
153     fout << text;
154 
155     fin.close();
156     fout.close();
157 }
158 
159 int main()
160 {
161     cout << "请输入字符进行下述操作：" << endl << endl;
162     while (1)
163     {
164         char tag;
165         showMenu();
166         cin >> tag;
167         switch (tag)
168         {
169         case ‘I‘:
170             Initialization();
171             break;
172         case ‘E‘:
173             Encoding();
174             break;
175         case ‘D‘:
176             Decoding();
177             break;
178         case ‘Q‘:
179             return 0;
180         case ‘W‘:
181             WriteText();
182             break;
183         default:
184             cout << "请输入正确的字符!" << endl;
185             cin >> tag;
186             break;
187         }
188     }
189     
190     return 0;
191 }