一個文字檔案，檔案很大，記錄了使用者搜尋關鍵詞，按照搜尋時間寫進文字，要求統計出其中最頻繁出現的前10個詞，請給出思想。

1. 建立Trie樹，記錄每顆樹的出現次數，O(n*le); le:平均查詢長度

2. 維護一個10的小頂堆，O(n*lg10);

3. 總複雜度： O(n*le) + O(n*lg10);

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#define WORD_NUM          256
struct trie_node {
	struct trie_node *node[WORD_NUM];
	int value;
	int count;
};
 
struct heap_node {
	char *word;
	int count;
};
 
void adjust_heap(struct heap_node *h, int len, int pos);
void create_heap(struct heap_node *h, int len);
void heap_sort(struct heap_node *h, int len);
int heap_insert_node(struct heap_node *h, int len, struct heap_node n);
void heap_insert_word(struct heap_node *h, int len, char *word, int count);
void destroy_heap(struct heap_node *h, int len);
void show_top_ten_word(struct heap_node *h, int len);
 
struct trie_node *create_trie_node(int value);
int trie_insert_word(struct trie_node *root, unsigned char *word);
void destory_trie_tree(struct trie_node *root);
 
void adjust_heap(struct heap_node *h, int len, int pos)
{
	int r, l, mark;
 
	l = 2 * pos;
	r = l + 1;
	mark = pos;
	if (l >= len) {
		return;
	}
 
	if ( h[mark].count > h[l].count) {
		mark = l;
	}
	if (r < len && h[mark].count > h[r].count) {
		mark = r;
	}
	if (mark != pos) {
		struct heap_node tmp;
		tmp = h[mark];
		h[mark] = h[pos];
		h[pos] = tmp;
		adjust_heap(h, len, mark);
	}
}	
 
void create_heap(struct heap_node *h, int len) 
{
	int range = len / 2;
	
	while (range >= 0) {
		adjust_heap(h, len, range--);
	}
}
 
void heap_sort(struct heap_node *h, int len) 
{
	struct heap_node n;
	create_heap(h, len);
	while (len > 0) {
		len--;
		n = h[len];
		h[len] = h[0];
		h[0] = n;
		adjust_heap(h, len, 0);
	}
}
 
void heap_insert_word(struct heap_node *h, int len, char *word, int count) 
{
	struct heap_node n;
	int size = strlen(word) + 1;
	n.word = malloc(size);
	n.count = count;
	memcpy(n.word, word, size);
	if (heap_insert_node(h, len, n) != 0) {
		free(n.word);
	}
}	
 
/* 不需要插入堆中和已經存在堆中 return -1, 插入返回 0 */
int heap_insert_node(struct heap_node *h, int len, struct heap_node n)
{
	int i;
	if (h[0].count > n.count) {
		return -1;
	}
	
	for (i = 0; i < len; i++) {
		if (strcmp(h[i].word, n.word) == 0) {
			h[i].count = n.count;
			break;
		}
	}
	if (i == len) {
		free(h[0].word);
		h[0] = n;
		adjust_heap(h, len, 0);
		return 0;
	}
	else {
		adjust_heap(h, len, i);
		return -1;
	}
}
void destroy_heap(struct heap_node *h, int len)
{
	while (len > 0) {
	   free(h[--len].word);
	}
	free(h);
	h = NULL;
}	
 
void show_top_ten_word(struct heap_node *h, int len)
{
	int i;
	heap_sort(h, len);
	for (i = 0; i < len; i++) {
		printf("%-8d %s\n", h[i].count, h[i].word);
	}
}
 
struct trie_node *create_trie_node(int value)
{
	struct trie_node * node = calloc(1, sizeof(struct trie_node));
	node->value = value;
	return node;
}
int trie_insert_word(struct trie_node *root, unsigned char *word) 
{
	struct trie_node *n;
	while (*word != 0) {
		n = root->node[*word];
		if (n == NULL) {
			n = create_trie_node(*word);
			root->node[*word] = n;
		}
		root = n;
		word++;
	}
	root->count++;
	return root->count;
}
void destroy_trie_tree(struct trie_node *root) 
{
	int i;
	if (root == NULL) {
		return;
	}
	for (i = 0; i < WORD_NUM; i++) {
		destroy_trie_tree(root->node[i]);
	}
	free(root);
}
 
int main(int argc, char *argv[])
{
	FILE *fp;
	struct trie_node *root;
	struct heap_node *h;
	int heap_len;	
	char line[1024];
	if (argc != 2) {
		return 0;
	}
 
	root = malloc(sizeof(struct trie_node));
	heap_len = 10;
	h = calloc(heap_len, sizeof(struct heap_node));
 
	fp = fopen(argv[1], "r");
	if (fp == NULL) {
		return 0;
	}
	int start = 0;
	while (fgets(line, sizeof(line), fp)) {
		int count;
		int word_len = strlen(line) - 1;
		line[word_len] = 0;
		count = trie_insert_word(root, (unsigned char *) line);
		if (start < heap_len) {
			int i;
			for (i = 0; i < start; i++) {
				if (strcmp(h[i].word, line) == 0) {
					h[i].count = count;
					break;
				}
			}
			if (i == start) {
				h[start].word = malloc(word_len);
				memcpy(h[start].word, line, word_len);
				h[start].count = count;
				start++;
				create_heap(h, start);		
			}
		}
		else {
			heap_insert_word(h, heap_len, line, count);
		}
 
	}	
	fclose(fp);
	heap_len = start;
	show_top_ten_word(h, heap_len);
	destroy_heap(h, heap_len);
	destroy_trie_tree(root);
	return 0;
}
 

原文