HuffmanTree

huffmanTree.h

#include <STDIO.H>
#include <STDLIB.H>
#include <MALLOC.H>
#include <STRING.H>

#define MAXSIZE 10

typedef struct
{
    unsigned int weight;
    unsigned int left,right,parent;
}HTNode,* HuffmanTree;

typedef char * * HuffmanCode;

void Select(HuffmanTree HT,int end,int &s1,int &s2);

void HuffmanCoding(HuffmanTree &HT,HuffmanCode &HC,int w[],int n)
{
    if(n <= 1)
    {
        return;
    }

    int m = 2*n-1,i,s1 = 1,s2 = 2;
    char *col;
    HT = (HuffmanTree)malloc(sizeof(HTNode)*(m+1));//这里0号单元没有使用
    HuffmanTree pt = HT;
    pt++;

    for(i = 1;i <= n;i++,w++,pt++)
    {
        pt->weight = *w;
        pt->left = 0;
        pt->right = 0;
        pt->parent = 0;
    }
    for(;i <= m;i++,pt++)
    {
        pt->weight = 0;
        pt->left = 0;
        pt->right = 0;
        pt->parent = 0;
    }

    for(i = n+1;i <= m;i++)//构造哈夫曼树
    {
        Select(HT,i-1,s1,s2);
        HT[i].left = s1;
        HT[i].right = s2;
        HT[i].weight = HT[s1].weight + HT[s2].weight;
        HT[s1].parent = i;
        HT[s2].parent = i;
    }

    //---第一种方法求哈夫曼编码,逆序
    /*
    HC = (HuffmanCode)malloc(sizeof(char *)*(n+1));
    col = (char *)malloc(sizeof(char)*n);
    col[n-1] = '\0';

    for(i = 1;i <= n;i++)
    {
        unsigned int start = n-1,p,f;
        p = f = i;
        while(HT[f].parent != 0)
        {
            f = HT[f].parent;
            if(HT[f].left == p)
            {
                col[--start] = '0';
            }
            else if(HT[f].right == p)
            {
                col[--start] = '1';
            }
            p = f;
        }
        HC[i] = (char *)malloc(sizeof(char)*(n-start));
        strcpy(HC[i],&col[start]);
        printf("%s\n",HC[i]);
    }

    free(col);
    */

    //---第二种方法求哈夫曼编码，正序
    for(i = 1;i <= m;i++)
    {
        HT[i].weight = 0;
    }

    col = (char *)malloc(sizeof(char)*n);
    HC = (HuffmanCode)malloc(sizeof(char *)*(n+1));
    //p作为循环终止条件，当遍历完成后p会退回到树根的parent即0，此时应该终止循环，而往下倒叶子节点时是不会为0的，因此可以作为循环条件
    int p = m,colen = 0;

    while(p)
    {
        if(HT[p].weight == 0)
        {
            HT[p].weight = 1;
            if(HT[p].left != 0)
            {
                p = HT[p].left;
                col[colen++] = '0';
            }
            else if(HT[p].right == 0)
            {
                HC[p] = (char *)malloc(sizeof(char)*(colen+1));
                strncpy(HC[p],col,colen);
                HC[p][colen] = '\0';
            }
        }
        else if(HT[p].weight == 1)
        {
            HT[p].weight = 2;
            if(HT[p].right != 0)
            {
                p = HT[p].right;
                col[colen++] = '1';
            }
        }
        else
        {
            HT[p].weight = 0;
            p = HT[p].parent;
            colen--;//变量名写准了，不能写错
        }
    }

}

void Select(HuffmanTree HT,int end,int &s1,int &s2)//从1到end之间选择最小的2个元素的下标
{
    int i = 1;
    unsigned int min1,min2;//min1和min2存放parent为0的最小的2个元素

    while(HT[i].parent != 0 && i <= end)//寻找第一个未访问的元素下标,if还是while一定要判断准确了，脑子清楚，不要犯低级错误
    {
        i++;
    }
    if(i == end+1)
    {
        return;
    }
    s1 = i;
    min1 = HT[i].weight;
    i++;
    while(HT[i].parent != 0 && i <= end)//寻找第二个未访问的元素下标，！还是不！一定要判断准确了才行，逻辑要理清楚
    {
        i++;
    }
    if(i == end+1)
    {
        return;
    }
    s2 = i;
    min2 = HT[i].weight;
    i++;
    if(min1 > min2)
    {
        unsigned int temp = min1;
        min1 = min2;
        min2 = temp;
        temp = s1;
        s1 = s2;
        s2 = temp;
    }
    for(;i <= end;i++)
    {
        if(HT[i].parent == 0)
        {
            if(HT[i].weight < min1)
            {
                s2 = s1;
                s1 = i;
                min2 = min1;
                min1 = HT[i].weight;
            }
            else if(HT[i].weight < min2)
            {
                s2 = i;
                min2 = HT[i].weight;
            }
        }
    }
}

main.cpp

#include "huffmanTree.h"

int main()
{
    int a[4] = {4,2,1,5};
    HuffmanTree ht;
    HuffmanCode hc;
    HuffmanCoding(ht,hc,a,4);
    for(int i = 1;i <= 4;i++)
    {
        //printf("%d  %s \n",ht[i].weight,hc[i]);
        printf("%s\n",hc[i]);
    }

    system("pause");
    return 0;
}