帮我用C语言写一个按前序遍历方法输出哈夫曼编码的函数

好的，以下是一个简单的按前序遍历输出哈夫曼编码的函数：

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

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

typedef struct {
    int size;
    int capacity;
    Node **arr;
} Heap;

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

Heap *newHeap(int capacity) {
    Heap *heap = (Heap *)malloc(sizeof(Heap));
    heap->size = 0;
    heap->capacity = capacity;
    heap->arr = (Node **)malloc(capacity * sizeof(Node *));
    return heap;
}

void swap(Node **a, Node **b) {
    Node *temp = *a;
    *a = *b;
    *b = temp;
}

void heapify(Heap *heap, int i) {
    int smallest = i;
    int left = 2 * i + 1;
    int right = 2 * i + 2;
    if (left < heap->size && heap->arr[left]->freq < heap->arr[smallest]->freq) {
        smallest = left;
    }
    if (right < heap->size && heap->arr[right]->freq < heap->arr[smallest]->freq) {
        smallest = right;
    }
    if (smallest != i) {
        swap(&heap->arr[i], &heap->arr[smallest]);
        heapify(heap, smallest);
    }
}

void insertHeap(Heap *heap, Node *node) {
    if (heap->size == heap->capacity) {
        return;
    }
    int i = heap->size;
    heap->arr[i] = node;
    heap->size++;
    while (i > 0 && heap->arr[(i - 1) / 2]->freq > heap->arr[i]->freq) {
        swap(&heap->arr[i], &heap->arr[(i - 1) / 2]);
        i = (i - 1) / 2;
    }
}

Node *extractMin(Heap *heap) {
    if (heap->size == 0) {
        return NULL;
    }
    Node *min = heap->arr[0];
    heap->arr[0] = heap->arr[heap->size - 1];
    heap->size--;
    heapify(heap, 0);
    return min;
}

void buildHeap(Heap *heap) {
    int n = heap->size;
    for (int i = n / 2 - 1; i >= 0; i--) {
        heapify(heap, i);
    }
}

void printCodes(Node *root, int arr[], int top) {
    if (root->left) {
        arr[top] = 0;
        printCodes(root->left, arr, top + 1);
    }
    if (root->right) {
        arr[top] = 1;
        printCodes(root->right, arr, top + 1);
    }
    if (!root->left && !root->right) {
        printf("%c: ", root->ch);
        for (int i = 0; i < top; i++) {
            printf("%d", arr[i]);
        }
        printf("\n");
    }
}

void huffmanCodes(char data[], int freq[], int size) {
    Heap *heap = newHeap(size);
    for (int i = 0; i < size; i++) {
        Node *node = newNode(data[i], freq[i]);
        insertHeap(heap, node);
    }
    while (heap->size > 1) {
        Node *left = extractMin(heap);
        Node *right = extractMin(heap);
        Node *parent = newNode('$', left->freq + right->freq);
        parent->left = left;
        parent->right = right;
        insertHeap(heap, parent);
    }
    int arr[100], top = 0;
    printCodes(extractMin(heap), arr, top);
}

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]);
    huffmanCodes(data, freq, size);
    return 0;
}

这个函数接受三个参数：一个字符数组 `data`，一个整数数组 `freq`，以及一个整数 `size`。`data` 数组存储了要编码的字符，`freq` 数组存储了每个字符出现的频率，`size` 是数组的大小。函数首先构建哈夫曼树，然后按前序遍历输出每个字符的编码。在这个函数中，我们使用了一个小根堆来构建哈夫曼树。