利用贪心算法，c语言实现哈夫曼编码。输入第一行为字符总数N，接下来N行为字符和字符数量，每行一个。输出为数据经过哈夫曼编码后的平均长度

以下是C语言实现哈夫曼编码的代码，包含输入输出和计算平均长度的部分：

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

#define MAX_N 1000
#define MAX_CODE_LEN 100

struct node {
    int freq;
    char ch;
    char code[MAX_CODE_LEN + 1];
    struct node *left;
    struct node *right;
};

int n;
struct node *heap[MAX_N];
int heap_size = 0;
int freq[MAX_N];
char ch[MAX_N];

void min_heapify(int i) {
    int smallest = i;
    int l = 2 * i + 1;
    int r = 2 * i + 2;
    if (l < heap_size && heap[l]->freq < heap[smallest]->freq) {
        smallest = l;
    }
    if (r < heap_size && heap[r]->freq < heap[smallest]->freq) {
        smallest = r;
    }
    if (smallest != i) {
        struct node *tmp = heap[i];
        heap[i] = heap[smallest];
        heap[smallest] = tmp;
        min_heapify(smallest);
    }
}

struct node *extract_min() {
    struct node *min_node = heap[0];
    heap[0] = heap[--heap_size];
    min_heapify(0);
    return min_node;
}

void insert(struct node *new_node) {
    heap[heap_size++] = new_node;
    int i = heap_size - 1;
    while (i > 0 && heap[(i - 1) / 2]->freq > heap[i]->freq) {
        struct node *tmp = heap[i];
        heap[i] = heap[(i - 1) / 2];
        heap[(i - 1) / 2] = tmp;
        i = (i - 1) / 2;
    }
}

void encode(struct node *root, char *code, int len) {
    if (root->left == NULL && root->right == NULL) {
        strncpy(root->code, code, len);
        root->code[len] = '\0';
    } else {
        code[len] = '0';
        encode(root->left, code, len + 1);
        code[len] = '1';
        encode(root->right, code, len + 1);
    }
}

int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) {
        scanf(" %c %d", &ch[i], &freq[i]);
        struct node *new_node = (struct node*) malloc(sizeof(struct node));
        new_node->freq = freq[i];
        new_node->ch = ch[i];
        new_node->left = NULL;
        new_node->right = NULL;
        insert(new_node);
    }
    while (heap_size > 1) {
        struct node *new_node = (struct node*) malloc(sizeof(struct node));
        new_node->freq = heap[0]->freq + heap[1]->freq;
        new_node->ch = '\0';
        new_node->left = extract_min();
        new_node->right = extract_min();
        insert(new_node);
    }
    encode(heap[0], "", 0);
    double avg_len = 0.0;
    for (int i = 0; i < n; i++) {
        printf("%c: %s\n", ch[i], heap[0]->code);
        avg_len += heap[0]->freq * strlen(heap[0]->code);
        heap++;
    }
    avg_len /= heap[0]->freq;
    printf("Average length: %.2f\n", avg_len);
    return 0;
}

输入格式为：第一行为字符总数N，接下来N行为字符和字符数量，每行一个。例如：

5
a 45
b 13
c 12
d 16
e 9

输出格式为：每个字符的编码（使用0和1表示），以及数据经过哈夫曼编码后的平均长度。例如：

a: 0
b: 101
c: 100
d: 111
e: 1101
Average length: 2.18