C++ 哈夫曼树（压缩、加密实现代码）

在以前写LZW压缩算法的时候，遇到很多难受的问题，基本上都在哈夫曼编码中解决了，虽然写这代码很费神，但还是把代码完整的码出来了，毕竟哈夫曼这个思想确实很牛逼。哈夫曼树很巧妙的解决了当时我在LZW序列化的时候想解决的问题，就是压缩后文本的分割。比如用lzw编码abc，就是1,2,3。但这个在存为文件的时候必须用分割符把1,2,3分割开，非常浪费空间，否则会和12 23 123 产生二义性。而哈夫曼树，将所有char分布在叶节点上，在还原的时候，比如1101110，假设110是叶节点，那么走到110的时候就可以确定，已经走到尽头，回到根节点继续走，这样就避免了字符的分割，全部用1010101010101这样的路径表示字符，可以将8位压缩为1个char进行存储。在构造树的时候，将出现率高的char放在上面，这样路径就很短，自然就节省了存储空间。虽然哈夫曼压缩效率不是最高的，但还算比较乐观的。

哈夫曼除了压缩以外还可以用于加密，在将文本用哈夫曼编码时，需持久化生成的char计数链表结构，这样才能还原出树结构，而解码时路径正是依赖于树结构的。也就是说，这种编码是属于约定形式的编码，在编码时用原文本产生树结构，而存储的是树路径，解码的时候缺少树或树结构与原先不相符都是无法完成解码的，就好比，我用10代表a，你存的是10，你将10解释为 b或c等等都是不正确的。由于转换为了char存储，所以还需持久化最后填充的数目、文本长度，才能还原出原先的01表示的文本格式

这个代码有一定缺陷，由于当时考虑的是对文本进行处理，当文件中有char='\0' 时会出现错误，这个代码打的很费神，就不继续修复了，如有需要，可自行更改，解决的办法应该挺多的

先来个运行图：

源代码

#include<iostream>#include<sstream>#include<fstream>void WriteFile(char* path,const char* content,int length,bool append=false);using namespace std;struct Node{ char data;Node* left;Node* right; };struct L_Node{int count;Node* node;L_Node* next;};Node* AddNode(int count,char data,L_Node*& first){L_Node* lnode=new L_Node();lnode->count=count;Node* node=new Node();node->data=data;node->left=0;node->right=0;lnode->node=node;if(first==0){first=lnode;}else{if(lnode->count<first->count){lnode->next=first;first=lnode;}else{L_Node* iter=first;while(iter->next!=0&&iter->next->count<lnode->count){iter=iter->next;}if(iter->next==0){iter->next=lnode;lnode->next=0;}else{lnode->next=iter->next;iter->next=lnode;}}}return node;}void SaveLNodes(L_Node* first){stringstream ss;while(first!=0){ss<<(int)(unsigned char)first->node->data<<':'<<first->count<<' ';first=first->next;}WriteFile("nodes.txt",ss.str().c_str(),ss.str().length());}void GetLNodes(L_Node*& first){char temp[32];ifstream in;in.open("nodes.txt",ios::in|ios::binary);while(!in.eof()){temp[0]=0;in>>temp;if(strlen(temp)>0){char* data=strtok(temp,":");char* count=strtok(0,":");AddNode(atoi(count),atoi(data),first);}}}void BuildSortedList(char* content,L_Node*& first,int length){int array[256]={0};for(int i=0;i<length;i++){array[(unsigned char)content[i]]++;}for(int i=0;i<256;i++){if(array[i]>0){AddNode(array[i],(char)i,first);}}SaveLNodes(first);}void BuildTree(L_Node*& first,Node*& root){//get l1->node,l2->node,remove l1,l2,then put l3 into list,then set l3->left and l3->rightif(first->next==0){Node* node=new Node();root=node;root->right=0;node=new Node();node->data=first->node->data;node->left=0;node->right=0;root->left=node;delete first;return;} while(first->next!=0){int count=first->count+first->next->count;Node* node1=first->node;L_Node* temp=first;first=first->next;delete temp;Node* node2=first->node;temp=first;delete temp;first=first->next;root=AddNode(count,0,first);root->left=node1;root->right=node2;//cout<<(int)node1->data<<':'<<(int)node2->data<<endl;}delete first;}void PreOrderTraversal(Node* node,char* track,int branch,char** table){if(node!=0){char* track2=0;if(branch==0){track2=new char[strlen(track)+2];sprintf(track2,"%s0\0",track);}else if(branch==1){track2=new char[strlen(track)+2];sprintf(track2,"%s1\0",track);}else{track2=new char[strlen(track)+1];sprintf(track2,"%s\0",track);}if(node->data!=0){table[(unsigned char)node->data]=track2;}PreOrderTraversal(node->left,track2,0,table);PreOrderTraversal(node->right,track2,1,table);if(node->data==0){delete track2;}}}void PreOrderTraversal(Node* node){if(node!=0){cout<<(int)(unsigned char)node->data<<endl;PreOrderTraversal(node->left);PreOrderTraversal(node->right);}}char* Encode(const char* content,char** table,int length){stringstream ss;for(int i=0;i<length;i++){if((unsigned char)content[i]==0){}else{ss<<table[(unsigned char)content[i]];}} char* encoded_content=new char[ss.str().length()+1];memcpy(encoded_content,ss.str().c_str(),ss.str().length());encoded_content[ss.str().length()]=0;return encoded_content;}int BinToDec(char* bin_content){int number=0;int cur=1;for(int i=7;i>=0;i--){number+=(bin_content[i]-'0')*cur;cur*=2;}return number;} char* BinToCharText(const char* bin_content,int& fill_count,int& save_length){int length=strlen(bin_content);fill_count=8-length%8;if(fill_count>0){char* temp=new char[length+fill_count+1];char temp1[fill_count];for(int i=0;i<fill_count;i++){temp1[i]='0';}sprintf(temp,"%s%s",bin_content,temp1);temp[length+fill_count]=0;bin_content=temp;}length+=fill_count;save_length=length/8;char* text=new char[length/8+1];for(int i=0;i<length;i+=8){char temp[8]; memcpy(temp,bin_content+i,8); text[i/8]=(char)BinToDec(temp); }text[length/8]=0;if(fill_count>0){delete bin_content;}return text;}char* DecToBin(int num){char* bin=new char[8];if(num<0){num=256+num;}for(int i=7;i>=0;i--){bin[i]=num%2+'0';num/=2;}return bin;}char* CharTextToBin(char* text,int fill_count,int save_length){int length=save_length;char* content=new char[8*length+1];int pos=0;for(int i=0;i<length;i++){ int number=text[i];char* bin=DecToBin(number);memcpy(content+pos,bin,8);pos+=8;delete bin;}content[8*length-fill_count]=0;return content;}char* Decode(const char* encode_content,Node* tree){stringstream ss;Node* node=tree;for(int i=0;i<strlen(encode_content);i++){if(encode_content[i]=='0'){node=node->left;}else if(encode_content[i]=='1'){node=node->right;}if(node->data!=0){ss<<node->data;node=tree;}}char* decode_content=new char[ss.str().length()+1];memcpy(decode_content,ss.str().c_str(),ss.str().length());decode_content[ss.str().length()]=0;return decode_content;}void ReleaseTable(char** table){for(int i=0;i<256;i++){if(table[i]!=0){delete table[i];}}}void PostOrderTraversal(Node* node){if(node!=0){PostOrderTraversal(node->left);PostOrderTraversal(node->right);delete node;}} char* ReadFile(char* path,long& length){char* content=0;ifstream in;in.open(path,ios::in|ios::binary);in.seekg(0,ios::end);length=in.tellg();content=new char[length+1];in.seekg(0,ios::beg);int i=0;while(!in.eof()){content[i++]=in.get();}content[length]=0;in.close();return content;}char* ReadFile(char* path,int& fill_count,int& save_length){char* content=0;ifstream in;in.open(path,ios::in|ios::binary);in>>fill_count>>save_length;long cur=in.tellg()+(long)1;in.seekg(0,ios::end);long length=in.tellg()-cur;content=new char[length+1];in.seekg(cur,ios::beg);int i=0;while(!in.eof()){content[i++]=in.get();}content[length]=0;in.close();return content;}void WriteFile(char* path,const char* content,int length,bool append){ofstream out;if(append){out.open(path,ios::out|ios::binary|ios::app);}else{out.open(path,ios::out|ios::binary);}  out.write(content,length); out.close();}int main(){long length;char* content=ReadFile("content.txt",length);L_Node* first=0;BuildSortedList(content,first,length); //create nodes list and save to nodes file//GetLNodes(first);//get and recreate nodes from fileNode* root=0;//used for buildtable and decodeBuildTree(first,root);//build tree by nodes list and release sorted listchar* table[256]={//build table,used for encode0};PreOrderTraversal(root,"",-1,table);//create table char* encode_content=Encode(content,table,length);//convert content to encoded bin text cout<<encode_content<<endl; delete content;  ReleaseTable(table);//release table when encode finishedint fill_count; int save_length; char* save_text=BinToCharText(encode_content,fill_count,save_length);//convert encoded bin text to char text and save these text to file delete encode_content; char head_info[32]; sprintf(head_info,"%d %d ",fill_count,save_length); WriteFile("encoded_content.txt",head_info,strlen(head_info));WriteFile("encoded_content.txt",save_text,save_length,true);delete save_text;save_text=ReadFile("encoded_content.txt",fill_count,save_length);//read fill_count、save_length、encoded char text from file char* bin_text= CharTextToBin(save_text,fill_count,save_length);//convert char text to bin textdelete save_text;char* decode_content=Decode(bin_text,root);//decode by bin_text and treecout<<decode_content<<endl;delete bin_text;delete decode_content;PostOrderTraversal(root);//release treereturn 0;}