哈夫曼编码 C++实现

首先，根据输入的字符串确定每个字母的频率，也就是权值，然后构造哈夫曼树，进行编码。解码就是从根节点不断往下查找，直到叶节点的过程。看哪个字符与从某序列匹配。

#include <iostream>
#include <map>
#include <queue>
using namespace std;

struct node{   //哈夫曼树的结点
    char ch;
    int frequent;
    node *lchild,*rchild;
    node(char c=0,double f=0,node *l=NULL,node *r=NULL):ch(c),frequent(f),lchild(l),rchild(r){}   //构造函数
};

struct cmp1{   //比较函数，根据字母出现的频率按从小到大排列
    bool operator()(node *&a,node *&b){
        return a->frequent > b->frequent;
    }
};

node * createTree(string str){  //构造哈夫曼树
    map<char,int>charSet;
    for(int i=0;i<str.length();i++)   //map结构保存字母出现的频次
        charSet[str[i]]++;
    priority_queue<node*,vector<node*>,cmp1>que;  //优先队列，按频次入队
    for(map<char,int>::iterator p = charSet.begin();p!=charSet.end();p++){
        que.push(new node(p->first,p->second));
    }
    while(que.size()>1){
        node *l = que.top();
        que.pop();
        node *r = que.top();  //选出权值最小的两个点，然后合并
        que.pop();
        node * newnode = new node(0,l->frequent+r->frequent,l,r);
        que.push(newnode);
    }
    return que.top();  //返回的是哈夫曼树中的顶层节点
}

void printInfo(const node* tree,string code){
    if(tree->lchild == NULL && tree->rchild == NULL){
        cout<<tree->ch<<":"<<code<<endl;
        return;
    }
    if(tree->lchild != NULL)   printInfo(tree->lchild,code+'0');  //向左走，为0
    if(tree->rchild != NULL)   printInfo(tree->rchild,code+'1');  //向右走，为1
}

string decode(const node *tree,string str){
    string ret = "";
    const node *p = tree;
    for(int i=0;i<str.length();i++){
        p = str[i] == '0'?p->lchild:p->rchild;
        if(p->lchild == NULL && p->rchild == NULL){    //看是否到叶节点
            ret += p->ch;
            p = tree;  //从根节点开始重新找下一个字母
        }
    }
    return ret;
}

void deleteTree(node *tree){   //释放空间
    if(tree->lchild != NULL)   deleteTree(tree->lchild);
    if(tree->rchild != NULL)   deleteTree(tree->rchild);
    deleteTree(tree);
}

int main(){
    string encodeStr = "aaaaaabbbbccddd";
    node *tree = createTree(encodeStr);
    printInfo(tree,"");
    string decodeStr = "010110111";
    string str = decode(tree,decodeStr);   //解码
    cout<<decodeStr<<":"<<str<<endl;
    return 0;
}