C++ 哈夫曼树对文件压缩、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->right
  if(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 file 

  Node* root=0;//used for buildtable and decode
  BuildTree(first,root);//build tree by nodes list and release sorted list 

  char* table[256]={//build table,used for encode
    0
  }; 

  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 finished 

  int 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 text
  delete save_text; 

  char* decode_content=Decode(bin_text,root);//decode by bin_text and tree
  cout<<decode_content<<endl;
  delete bin_text;
  delete decode_content; 

  PostOrderTraversal(root);//release tree 

  return 0;
} 

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