写出c语言构造哈夫曼树的代码

下面是 C 语言构造哈夫曼树的代码：

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

#define MAX_NODE_COUNT 256  // 字符集大小为 256

typedef struct Node {
    char c;
    int freq;
    struct Node *left, *right;
} Node;

typedef struct MinHeap {
    int count;
    Node **array;
} MinHeap;

Node *new_node(char c, int freq, Node *left, Node *right) {
    Node *node = (Node *)malloc(sizeof(Node));
    node->c = c;
    node->freq = freq;
    node->left = left;
    node->right = right;
    return node;
}

MinHeap *create_min_heap(int size) {
    MinHeap *min_heap = (MinHeap *)malloc(sizeof(MinHeap));
    min_heap->count = 0;
    min_heap->array = (Node **)malloc(size * sizeof(Node *));
    return min_heap;
}

void swap(Node **l, Node **r) {
    Node *temp = *l;
    *l = *r, *r = temp;
}

void min_heapify(MinHeap *min_heap, int index) {
    int min = index, left = index * 2 + 1, right = index * 2 + 2;
    if (left < min_heap->count && min_heap->array[min]->freq > min_heap->array[left]->freq)
        min = left;
    if (right < min_heap->count && min_heap->array[min]->freq > min_heap->array[right]->freq)
        min = right;
    if (min != index) {
        swap(&min_heap->array[min], &min_heap->array[index]);
        min_heapify(min_heap, min);
    }
}

int is_single_node(MinHeap *min_heap) {
    return min_heap->count == 1;
}

Node *extract_min(MinHeap *min_heap) {
    Node *node = min_heap->array[0];
    min_heap->array[0] = min_heap->array[min_heap->count - 1];
    --min_heap->count;
    min_heapify(min_heap, 0);
    return node;
}

void insert(MinHeap *min_heap, Node *node) {
    ++min_heap->count;
    int index = min_heap->count - 1;
    while (index > 0 && node->freq < min_heap->array[(index - 1) / 2]->freq) {
        min_heap->array[index] = min_heap->array[(index - 1) / 2];
        index = (index - 1) / 2;
    }
    min_heap->array[index] = node;
}

void build_min_heap_from_freqs(int freqs[]) {
    MinHeap *min_heap = create_min_heap(MAX_NODE_COUNT);
    for (int i = 0; i < MAX_NODE_COUNT; ++i) {
        if (freqs[i] > 0) {
            Node *node = new_node((char)i, freqs[i], NULL, NULL);
            insert(min_heap, node);
        }
    }
    while (!is_single_node(min_heap)) {
        Node *left = extract_min(min_heap), *right = extract_min(min_heap);
        Node *node = new_node('\0', left->freq + right->freq, left, right);
        insert(min_heap, node);
    }
    Node *root = extract_min(min_heap);
}

void build_min_heap_from_file(char *filename) {
    FILE *fp = fopen(filename, "r");
    if (!fp) {
        fprintf(stderr, "Error: failed to open file `%s`\n", filename);
        exit(1);
    }
    int freqs[MAX_NODE_COUNT] = {};
    int c;
    while ((c = fgetc(fp)) != EOF) {
        ++freqs[c];
    }
    fclose(fp);
    build_min_heap_from_freqs(freqs);
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <filename>\n", argv[0]);
        return 1;
    }
    build_min_heap_from_file(argv[1]);
    return 0;
}