跑骚时刻 - C笔记：赫夫曼编码

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <conio.h>
#pragma warning(disable:4996)

typedef struct HuffmanTree
{
    int weight;//权值
    int parent;//父节点
    int left;//左子树
    int right;//右子树
};

typedef char *HuffmanCode;//Huffmancode编码

//从1-x个节点选择parent节点为0，权重最小的两个节点
void SelectNode(HuffmanTree *ht, int n, int *bt1, int *bt2){
    int i;
    HuffmanTree *ht1, *ht2, *t;
    ht1 = ht2 = NULL;//初始化两个节点为空
    for (i = 1; i <= n; ++i)//循环处理1-n个节点（包括叶节点和非叶节点）
    {
        if (!ht[i].parent)//父节点为空(节点的parent为0)
        {
            if (ht1 == NULL)//节点指针1为空
            {
                ht1 = ht + i;//指向第i个节点
                continue;//继续循环
            }
            if (ht2 == NULL)
            {
                ht2 = ht + i;
                if (ht1->weight > ht2->weight)//比较两个值的权重，使ht1指向权值大的
                {
                    t = ht2;
                    ht2 = ht1;
                    ht1 = t;
                }
                continue;//继续循环
            }
            if (ht1 && ht2)//若两个值都有效
            {
                if (ht[i].weight <= ht1->weight)//第i个节点权重小于ht1指向的节点
                {
                    ht2 = ht1;//ht2保存ht1,因为这时ht1指向的节点成为第2小的
                    ht1 = ht + i;
                }
                else if (ht[i].weight < ht2->weight)//若第i个节点权重小于ht2指向的权重
                {
                    ht2 = ht + i;
                }
            }
        }
    }
    if (ht1 > ht2)//增加比较，使二叉树左侧为叶节点
    {
        *bt2 = ht1 - ht;
        *bt1 = ht2 - ht;
    }
    else
    {
        *bt1 = ht1 - ht;
        *bt2 = ht2 - ht;
    }
}

void CreateTree(HuffmanTree *ht, int n, int *w){
    int i, m = 2 * n - 1;//总的节点总数
    int bt1, bt2;//二叉树节点序与
    if (n <= 1)//只有一个节点就无法创建
    {
        return;
    }
    for (i = 0; i <= n; ++i)//初始化节点
    {
        ht[i].weight = w[i - 1];
        ht[i].parent = 0;
        ht[i].left = 0;
        ht[i].right = 0;
    }
    for (; i <= m; ++i)//初始化后序节点
    {
        ht[i].weight = 0;
        ht[i].parent = 0;
        ht[i].left = 0;
        ht[i].right = 0;
    }
    for (i = n + 1; i <= m; ++i)//逐个计算非叶节点，创建Huffman树
    {
        SelectNode(ht, i - 1, &bt1, &bt2);
        ht[bt1].parent = i;
        ht[bt2].parent = i;
        ht[i].left = bt1;
        ht[i].right = bt2;
        ht[i].weight = ht[bt1].weight + ht[bt2].weight;
    }
}

//
void HuffmanCoding(HuffmanTree *ht, int n, HuffmanCode *hc){
    char *cd;
    int start, i;
    int current, parent;
    cd = (char*)malloc(sizeof(char)*n);//用来临时存放一个字符编码的结果
    cd[n - 1] = '\0';//设置字符串结束标志
    for (i = 1; i <= n; i++)
    {
        start = n - 1;
        current = i;
        parent = ht[current].parent;//获取当前节点的父节点；
        while (parent)
        {
            if (current == ht[parent].left)//若该节点的父节点是做左子树
            {
                cd[--start] = '0';//设置编码为0
            }
            else//若该节点是父节点的右子树
            {
                cd[--start] = '1';//设置编码为1
            }
            current = parent;//设置当前节点指向父节点
            parent = ht[parent].parent;//获取当前节点的父节点序号；
        }
        hc[i - 1] = (char*)malloc(sizeof(char)*(n - start));
        strcpy(hc[i - 1], &cd[start]);//复制生成生成的编码
    }
    free(cd);//释放编码占用的字符
}

void Encode(HuffmanCode *hc, char *alphabet, char *str, char *code){
    //将一个字符串转换为Huffman编码
    //hc为Huffman编码表，alphabet为对应的字母表，str为需要转换的字符串，code返回转换的结果
    int len = 0, i = 0, j;
    code[0] = '\0';
    while (str[i])
    {
        j = 0;
        while (alphabet[j] != str[i])
        {
            j++;
        }
        strcpy(code + len, hc[j]);//将对应字母的Huffman编码复制code指定位置
        len = len + strlen(hc[j]);//累加字符串长度
        i++;
    }
    code[len] = '\0';
}

void Decode(HuffmanTree *ht, int m, char *code, char *alphabet, char *decode){
    //将一个huffman编码组成的字符串转换为明文字符串
    //ht为huffman二叉树，m为字符数量，alphabet为对应的字母表，str需转换的字符串
    int position = 0, i, j = 0;
    m = 2 * m - 1;
    while (code[position])//字符串未结束
    {
        for (i = m; ht[i].left && ht[i].right; position++)
        {
            if (code[position] == '0')//编码位为0
            {
                i = ht[i].left;
            }
            else
            {
                i = ht[i].right;//处理右子树
            }
        }
        decode[j] = alphabet[i - 1];//得到一个字母
        j++;//处理下一个字符
    }
    decode[j] = '\0';//字符串结尾
}

//主函数
int main(void){
    int i, n = 4, m;
    char test[] = "DBDACDADCCDBDCBADBCABABA";
    char code[100], code1[100];
    char alphabet[] = { 'A', 'B', 'C', 'D', };//四个字符
    int w[] = { '5', '7', '2', '13' };//四个字符的权重
    HuffmanTree *ht;
    HuffmanCode *hc;
    m = 2 * n - 1;
    ht = (HuffmanTree *)malloc((m + 1)*sizeof(HuffmanTree));//申请内存，保存赫夫曼树
    if (!ht)
    {
        printf("内存分配失败！");
        exit(0);
    }
    hc = (HuffmanCode *)malloc(n*sizeof(char*));
    if (!hc)
    {
        printf("分配内存失败！");
        exit(0);
    }
    //创建赫夫曼树
    CreateTree(ht, n, w);
    HuffmanCoding(ht, n, hc);//根据赫夫曼树生成的赫夫曼编码
    for (i = 1; i <= n; i++)
    {
        printf("字母：%c,权重：%d,编码为：%s\n", alphabet[i - 1], ht[i].weight, hc[i - 1]);
    }
    Encode(hc, alphabet, test, code);//根据赫夫曼编码生成编码字符串
    printf("\n字符串：\n%s\n转换后为：\n%s\n", test, code);

    Decode(ht, n, code, alphabet, code1);//根据编码字符串生成解码后的字符串
    printf("\n编码：\n%s\n转换后为：\n%s\n", code, code1);
    _getch();
    return 0;
}