最优二叉树（哈夫曼树）、哈夫曼编码（HuffmanCoding）

//求哈夫曼编码的算法如下所示：
//-----哈夫曼树和哈夫曼编码的存储表示-----
typedef struct{
    unsigned int weight;
    unsigned int parent,lchild,rchild;
}HTNode,*HuffmanTree;
typedef char * * HuffmanCode;
//-----求哈夫曼编码的算法如下所示-----
void HuffmanCoding(HuffmanTree & HT, HuffmanCode &HC, int *w, int n){
    //w存放n个自负字符的权值（均>0）,构造哈夫曼树HT，并求出n个字符的哈夫曼编码HC
    if(n <= 1)  return;
    m = 2 * n - 1;
    HT = (HuffmanTree)malloc((m + 1) * sizeof(HTNode));
    for(p = HT + 1, i = 1; i <= n; ++i, ++p, ++w)   *p = {*w,0,0,0};
    for(; i <= m; ++i,++p)  *p = {0,0,0,0};
    for(i = n+1; i <= m; ++i){  //建哈夫曼树
        //在HT[1..i-1]选择parent为0且weight最小的两个结点，其序号分别为s1和s2.
        Select(HT,i-1,s1,s2);
        HT[s1].parent = i;  HT[s2].parent = i;
        HT[i].lchild = s1;  HT[i.rchild = s2;
        HT[i].weight = HT[sl].weight + HT[s2].weight;
    }
    //---从叶子到根逆向求每个字符的哈夫曼编码
    HC = (HuffmanCode)malloc((n + 1) * sizeof(char *)); //分配n个字符编码的头指针位置
    cd = (char *)malloc(n * sizeof(char));      //分配求编码的工作空间
    cd[n-1] = "\0";                             //编码结束符
    for(i=1; i <= n; ++i){                      //逐个字符求哈夫曼编码
        start = n-1;                            //编码结束符位置
        for(c = i, f = HT[i].parent; f != 0; c = f, f = HT[f].parent)//从叶子到根逆向求编码
            if(HT[f].lchild == c)   cd[--start] = '0';
            else cd[--start] = "1";
        HC[i] = (char *)malloc((n - start) * sizeof(char));//为敌第i个字符编码分配空间
        strcpy(HC[i],&cd[start]);               //把cd复制到HC
    }
    free(cd);               //释放工作空间
    //---无栈非递归变里哈夫曼树，求哈夫曼编码
    HC = (HuffmanCode)malloc((n + 1) * sizeof(char *)); 
    p = m;  cdlen = 0;
    for(i = 1; i <= m; ++i) HT[i].weight = 0;   //遍历哈夫曼树时用作结点状态标志
    while(p){
        if(HT[p].weight == 0){                  //向左
            HT[p].weight = 1;
            if(HT[p].lchild != 0)   {P = HT[P].lchild;  cd[cdlen++] = "0";}
            else if(HT[p].rchild == 0){         //登记叶子结点的字符的编码
                HC[p] = (char *)malloc((cd + 1) * sizeof (char));
                cd[cdlen] = "\0";   strcpy(HC[p],cd);//复制编码（串）
            }//else if
        }//if
        else if(HT[p].weight == 1){             //向右
            HT[p].weight = 2;
            if(HT[p].lchild != 0)   {p = HT[p].lchild;  cd[cdlen++] = "1";}
        }else{                                  //HT[p].weight == 2,退回
            HT[p].weight = 0;   p = HT[p].parent;   --cdlen;    //遇到父节点，编码长度减1
        }//else
    }//while
}