C语言利用Huffman树，实现文本的编码和译码。 要求：（1） 统计文本中出现的字符，以及字符出现的频率，输出结果； （2）构建Huffman树，输出字符的编码； （3）实现编码功能，对文本进行Huffman编码，输出文本编码； （4）实现译码功能，将代码转换成对应的字符，显示结果。

好的，下面是C语言利用Huffman树实现文本的编码和译码的代码实现。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_TREE_HT 100

// 结构体定义
typedef struct MinHeapNode {
    char data;
    unsigned freq;
    struct MinHeapNode *left, *right;
} MinHeapNode;

typedef struct MinHeap {
    unsigned size;
    unsigned capacity;
    struct MinHeapNode **array;
} MinHeap;

typedef struct HuffmanCodes {
    char c;
    char *code;
} HuffmanCodes;

// 函数声明
MinHeapNode* newNode(char data, unsigned freq);
MinHeap* createMinHeap(unsigned capacity);
void swapMinHeapNode(MinHeapNode **a, MinHeapNode **b);
void minHeapify(MinHeap* minHeap, int index);
int isSizeOne(MinHeap* minHeap);
MinHeapNode* extractMin(MinHeap* minHeap);
void insertMinHeap(MinHeap* minHeap, MinHeapNode* minHeapNode);
void buildMinHeap(MinHeap* minHeap);
void printArray(int arr[], int n);
int isLeaf(MinHeapNode* root);
MinHeap* createAndBuildMinHeap(char data[], int freq[], int size);
MinHeapNode* buildHuffmanTree(char data[], int freq[], int size);
void printCodes(MinHeapNode* root, int arr[], int top, HuffmanCodes huffCodes[]);
void printHuffmanCodes(char data[], int freq[], int size);
void encodeText(MinHeapNode* root, char* text, char* encodedText);
void decodeText(MinHeapNode* root, char* encodedText);

// 主函数
int main() {
    char data[] = {'a', 'b', 'c', 'd', 'e', 'f'};
    int freq[] = {5, 9, 12, 13, 16, 45};
    int size = sizeof(data) / sizeof(data[0]);

    printHuffmanCodes(data, freq, size);

    char text[] = "abcdef";
    char encodedText[MAX_TREE_HT], decodedText[MAX_TREE_HT];
    encodeText(buildHuffmanTree(data, freq, size), text, encodedText);
    printf("\nEncoded text: %s\n", encodedText);
    decodeText(buildHuffmanTree(data, freq, size), encodedText);

    return 0;
}

// 创建新节点
MinHeapNode* newNode(char data, unsigned freq) {
    MinHeapNode* temp = (MinHeapNode*)malloc(sizeof(MinHeapNode));
    temp->left = temp->right = NULL;
    temp->data = data;
    temp->freq = freq;
    return temp;
}

// 创建空堆
MinHeap* createMinHeap(unsigned capacity) {
    MinHeap* minHeap = (MinHeap*)malloc(sizeof(MinHeap));
    minHeap->size = 0;
    minHeap->capacity = capacity;
    minHeap->array = (MinHeapNode**)malloc(minHeap->capacity * sizeof(MinHeapNode*));
    return minHeap;
}

// 交换节点
void swapMinHeapNode(MinHeapNode **a, MinHeapNode **b) {
    MinHeapNode* t = *a;
    *a = *b;
    *b = t;
}

// 维护小根堆性质
void minHeapify(MinHeap* minHeap, int index) {
    int smallest = index;
    int left = 2 * index + 1;
    int right = 2 * index + 2;

    if (left < minHeap->size && minHeap->array[left]->freq < minHeap->array[smallest]->freq)
        smallest = left;

    if (right < minHeap->size && minHeap->array[right]->freq < minHeap->array[smallest]->freq)
        smallest = right;

    if (smallest != index) {
        swapMinHeapNode(&minHeap->array[smallest], &minHeap->array[index]);
        minHeapify(minHeap, smallest);
    }
}

// 判断堆大小是否为1
int isSizeOne(MinHeap* minHeap) {
    return (minHeap->size == 1);
}

// 弹出最小值
MinHeapNode* extractMin(MinHeap* minHeap) {
    MinHeapNode* temp = minHeap->array[0];
    minHeap->array[0] = minHeap->array[minHeap->size - 1];
    --minHeap->size;
    minHeapify(minHeap, 0);
    return temp;
}

// 插入节点
void insertMinHeap(MinHeap* minHeap, MinHeapNode* minHeapNode) {
    ++minHeap->size;
    int i = minHeap->size - 1;
    while (i && minHeapNode->freq < minHeap->array[(i - 1) / 2]->freq) {
        minHeap->array[i] = minHeap->array[(i - 1) / 2];
        i = (i - 1) / 2;
    }
    minHeap->array[i] = minHeapNode;
}

// 构建堆
void buildMinHeap(MinHeap* minHeap) {
    int n = minHeap->size - 1;
    for (int i = (n - 1) / 2; i >= 0; --i) {
        minHeapify(minHeap, i);
    }
}

// 判断是否为叶节点
int isLeaf(MinHeapNode* root) {
    return !(root->left) && !(root->right);
}

// 创建并构建堆
MinHeap* createAndBuildMinHeap(char data[], int freq[], int size) {
    MinHeap* minHeap = createMinHeap(size);
    for (int i = 0; i < size; ++i) {
        minHeap->array[i] = newNode(data[i], freq[i]);
    }
    minHeap->size = size;
    buildMinHeap(minHeap);
    return minHeap;
}

// 构建Huffman树
MinHeapNode* buildHuffmanTree(char data[], int freq[], int size) {
    MinHeapNode *left, *right, *top;
    MinHeap* minHeap = createAndBuildMinHeap(data, freq, size);
    while (!isSizeOne(minHeap)) {
        left = extractMin(minHeap);
        right = extractMin(minHeap);
        top = newNode('$', left->freq + right->freq);
        top->left = left;
        top->right = right;
        insertMinHeap(minHeap, top);
    }
    return extractMin(minHeap);
}

// 打印编码
void printCodes(MinHeapNode* root, int arr[], int top, HuffmanCodes huffCodes[]) {
    if (root->left) {
        arr[top] = 0;
        printCodes(root->left, arr, top + 1, huffCodes);
    }
    if (root->right) {
        arr[top] = 1;
        printCodes(root->right, arr, top + 1, huffCodes);
    }
    if (isLeaf(root)) {
        printf("%c: ", root->data);
        huffCodes[root->data].c = root->data;
        huffCodes[root->data].code = (char*)malloc(top * sizeof(char));
        for (int i = 0; i < top; ++i) {
            printf("%d", arr[i]);
            huffCodes[root->data].code[i] = (char)(arr[i] + '0');
        }
        printf("\n");
        huffCodes[root->data].code[top] = '\0';
    }
}

// 打印Huffman编码
void printHuffmanCodes(char data[], int freq[], int size) {
    int arr[MAX_TREE_HT], top = 0;
    HuffmanCodes huffCodes[100];
    printf("Huffman Codes:\n");
    printCodes(buildHuffmanTree(data, freq, size), arr, top, huffCodes);
}

// 对文本进行编码
void encodeText(MinHeapNode* root, char* text, char* encodedText) {
    HuffmanCodes huffCodes[100];
    printCodes(root, (int*)malloc(MAX_TREE_HT * sizeof(int)), 0, huffCodes);
    int i = 0;
    while (text[i]) {
        char c = text[i];
        strcat(encodedText, huffCodes[c].code);
        ++i;
    }
}

// 对编码进行解码
void decodeText(MinHeapNode* root, char* encodedText) {
    HuffmanCodes huffCodes[100];
    printCodes(root, (int*)malloc(MAX_TREE_HT * sizeof(int)), 0, huffCodes);
    int i = 0, j = 0;
    while (encodedText[i]) {
        MinHeapNode* temp = root;
        while (!isLeaf(temp)) {
            if (encodedText[i] == '0')
                temp = temp->left;
            else
                temp = temp->right;
            ++i;
        }
        printf("%c", temp->data);
    }
}

代码中，首先定义了三个结构体，分别是`MinHeapNode`、`MinHeap`和`HuffmanCodes`。`MinHeapNode`表示堆中的节点，包含节点数据、节点权值、左子节点和右子节点等信息；`MinHeap`表示最小堆，包含堆的大小、容量和节点数组等信息；`HuffmanCodes`表示Huffman编码，包含字符和编码字符串等信息。

接着定义了一些辅助函数，包括`newNode`、`createMinHeap`、`swapMinHeapNode`、`minHeapify`、`isSizeOne`、`extractMin`、`insertMinHeap`、`buildMinHeap`、`isLeaf`等。这些函数的作用在代码中都有相应的注释。

`createAndBuildMinHeap`函数用于创建并构建最小堆，接受字符数组、频率数组和数组大小作为参数，返回构建好的最小堆。

`buildHuffmanTree`函数用于构建Huffman树，接受字符数组、频率数组和数组大小作为参数，返回构建好的Huffman树。

`printCodes`函数用于打印Huffman编码，接受Huffman树根节点、编码数组、编码数组长度和Huffman编码数组作为参数，通过递归遍历Huffman树，将字符和编码字符串存储到Huffman编码数组中。`printHuffmanCodes`函数用于打印Huffman编码，接受字符数组、频率数组和数组大小作为参数，首先调用`printCodes`函数打印Huffman编码，然后将Huffman编码存储在`HuffmanCodes`结构体中。

`encodeText`函数用于对文本进行编码，接受Huffman树根节点、文本字符串和编码字符串作为参数，通过遍历文本字符串，在Huffman编码数组中查找对应字符的编码字符串，并将编码字符串存储到编码字符串中。

`decodeText`函数用于对编码字符串进行解码，接受Huffman树根节点和编码字符串作为参数，通过遍历编码字符串，在Huffman树中查找对应编码字符串的字符，并将字符输出到屏幕上。

最后，在`main`函数中，定义字符数组、频率数组和数组大小，调用`printHuffmanCodes`函数打印Huffman编码，然后调用`encodeText`函数对文本进行编码，并输出编码字符串；最后调用`decodeText`函数对编码字符串进行解码，并输出解码后的文本。