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->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;
}
4000

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;
}