trie树-《算法导论》学习笔记十四

引用一下百度百科的话吧：
Trie树，又称单词查找树，是一种树形结构，是一种哈希树的变种。典型应用是用于统计，排序和保存大量的字符串（但不仅限于字符串），所以经常被搜索引擎系统用于文本词频统计。它的优点是：利用字符串的公共前缀来减少查询时间，最大限度地减少无谓的字符串比较，查询效率比哈希树高。

这里构建了一棵字典树，每个结点有52个孩子指针，对应26个小写字母和26个大写字母，根节点不存储数据，一个单词从第一个字母开始经由根结点走对应分支进行插入和统计。

trie树结点卫星数据包含了字母、出现次数、是否构成一个单词，孩子指针就是一个52大小的trie树结点指针数组。

实现了几个操作：

1. 插入单词

遍历每个字母，从根结点出发，如果结点对应字母的孩子结点为空，就创建结点，出现次数为1，如果存在这个结点，出现次数就+1，并且如果单词结束，结束处的结点是否构成一个单词字段标识为构成

2. 遍历树，并打印所有单词和每个单词出现次数

3. 统计树，按给定的数字统计出现次数前几的单词

树统计，与遍历类似，用尾递归，并传入一个大于单词最大长度的数组来存储每个分支的单词，如果遇到结点能构成一个单词，就判断你单词个数，并以插入排序的方式插入创建的统计链表（类似打扑克的插排序）；
统计链表有更新操作，根据输入的统计前几的数字来维护这个链表该去掉哪些结点，该更新哪些结点的顺序等

---

获取单词来源为编写的一个简单单词随机生成代码，写入一个文件中，可指定单词最大长度，全大写/全小写/大小写均有，单词个数，单词范围（只支持a-*或A-*，例如5，就是生成a-e/A-E的单词）
贴代码：

随机生成单词

#include <stdio.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <time.h>#include <unistd.h>#include <errno.h>#include <string.h>#include <stdlib.h>int word_len = 0;int upper_low = 65;int lowwer_low = 97;// if letter_size = 5// it will generate a-e or A-E letter.int letter_size = 0;int random_letter(){    return rand() % letter_size;}int random_word(    char *word,    int opt ){       // minimum word'length is 3.    int true_word_len = rand() % word_len + 3;    int true_word_len1 = true_word_len;    while ( true_word_len-- ) {        char letter = 0;        if ( opt == 0 ) {            letter = random_letter() + lowwer_low;        } else if ( opt == 1 ) {            letter = random_letter() + upper_low;        } else {            int opt_case = rand() % 2;            if ( opt_case == 0 )                letter = random_letter() + lowwer_low;            else                 letter = random_letter() + upper_low;        }        word[true_word_len] = letter;    }    return true_word_len1;}void gen_word(    int fd,    int word_num,    int opt ){    char word[20] = {0};    int true_word_len = 0;    while ( word_num-- ) {        memset( word, 0, 20);        true_word_len = random_word( word, opt );        word[true_word_len] = '\n';        write( fd, word, true_word_len + 1 );    }}int main(    int argc,    char **argv ){    srand((int)time(NULL));    if ( argc != 5 ) {        printf("please input "                "word's length & "                "words' number & "                "word's range & "                "gen_case(0:lowwer case,1:upper case,other:both\n");        exit( 0 );    }    word_len = atoi( argv[1] );    int word_num = atoi( argv[2] );    letter_size = atoi( argv[3] );    int opt = atoi( argv[4] );    int fd = open("word.txt", O_RDWR | O_TRUNC, 0777);    gen_word( fd, word_num, opt );    close( fd );    return 0;}

trie树

#include <stdio.h>#include <unistd.h>#include <stdlib.h>#include <string.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <errno.h>#define MAX_CHILD_NUM 52#define UPPER_LOW 65#define UPPER_UP 90#define LOWER_LOW 97#define LOWER_UP 122#define PRINT(format, arg...) \do { \    printf("[%s/%d]:", __func__, __LINE__); \    printf(format, ##arg); \    printf("\n"); \}while(0) typedef struct trieTreeNode {    char letter;    int count;    int is_word;    struct trieTreeNode *next[MAX_CHILD_NUM];} trieTreeNode;typedef struct trieTree {    trieTreeNode *root;} trieTree;typedef struct count_data {    int order;    int count;    char string[20];    struct count_data *next;} count_data;int trans_letter_2_index(    char letter ){    int index = -1;    if ( letter >= LOWER_LOW         && letter <= LOWER_UP ) {        index = letter - LOWER_LOW + 26;    } else if ( letter >= UPPER_LOW         && letter <= UPPER_UP ) {        index = letter - UPPER_LOW;     } else {        PRINT("error letter input:%c", letter);        exit( 0 );    }    return index;}trieTreeNode *create_node(    char letter ){    trieTreeNode *node =         ( trieTreeNode * )calloc( 1, sizeof(trieTreeNode) );    node->letter = letter;    node->count = 0;    node->is_word = 0;}void insert(    trieTreeNode *root,    char *word ){    if ( root == NULL ) {        PRINT("root node is null.");        return;    }    int i = 0;    trieTreeNode *cur = root;    for ( i; word[i] != '\0'; i++ ) {        int next_index = trans_letter_2_index(word[i]);        //PRINT("letter:%c, index:%d", word[i], next_index);        if ( cur->next[next_index] == NULL ) {            cur->next[next_index] = create_node( word[i] );        } else {            //cur->next[next_index]->count += 1;        }        if ( word[i+1] == '\0' ) {            cur->next[next_index]->count += 1;            cur->next[next_index]->is_word = 1;        }        cur = cur->next[next_index];    }}// 删除链表所有结点void delete_list_all_node(    count_data *node ){    count_data *p = NULL;    while ( node ) {        p = node;        node = node->next;        free( p );    }}void print_list_all_node(    count_data *node ){    printf("\n");    node = node->next;    while ( node ) {        printf("[%d],count:%d\tword:%s\n",             node->order, node->count, node->string);        node = node->next;    }    printf("\n");}void update_insert_node(    count_data *insert_node ){    if ( !insert_node->next )        return;    count_data *print_p = insert_node;     if ( insert_node->order == 1 ) {        delete_list_all_node( insert_node->next );        insert_node->next = NULL;    } else if ( insert_node->order < 1 ) {        PRINT("ERROR!!!!!");        exit( 0 );    } else {        count_data *p = insert_node;        insert_node = insert_node->next;        while ( insert_node ) {            if ( insert_node->count < p->count ) {                insert_node->order = p->order - 1;            } else if ( insert_node->count > p->count ) {                PRINT("ERROR!!!cur->count:%d, pre->count:%d",                     insert_node->count, p->count);                exit( 0 );            } else {                insert_node->order = p->order;            }            if ( insert_node->order < 1 ) {                delete_list_all_node( insert_node );                p->next = NULL;                break;            }            p = insert_node;            insert_node = insert_node->next;        }    }}void list_insert(     char *tmp_word,    int cur_count,    int tail,    count_data *head,    int top_num ){    tmp_word[tail] = '\0';    count_data *new_data = ( count_data * )malloc( sizeof(count_data) );    new_data->count = cur_count;    memcpy( new_data->string, tmp_word, tail + 1 );    new_data->next = NULL;    //PRINT("count:%d\ttmp_word:%s, string:%s", cur_count, tmp_word, new_data->string);    if ( head->next == NULL ) {        head->next = new_data;        new_data->order = top_num;    } else if ( cur_count > head->next->count ) {        new_data->order = head->next->order;        new_data->next = head->next;        head->next = new_data;        update_insert_node( new_data );    } else {        while ( 1 ) {            head = head->next;            if ( head->next == NULL ) {                if ( head->order > 1 ) {                    head->next = new_data;                    if ( head->count == new_data->count )                         new_data->order = head->order;                    else                        new_data->order = head->order - 1;                    head->next = new_data;                } else if ( head->count > new_data->count ) {                    // 不插入                    free( new_data );                } else if ( head->count == new_data->count ) {                    head->next = new_data;                    new_data->order = head->order;                } else if ( head->count < new_data->count ) {                    // 此种情况只有求出现次数最多的前1个单词时有                    head->count = new_data->count;                    free( new_data );                }                break;            } else if ( head->count >= cur_count                 && head->next->count < cur_count ) {                new_data->next = head->next;                head->next = new_data;                new_data->order = head->order;                update_insert_node( new_data );                break;            }        }    }}void find_top_count1(    trieTreeNode *root,    char *tmp_word,    int tail,    count_data *head,     int top_num ){    if ( !root )        return;    tmp_word[tail] = root->letter;    tail++;    if ( root->is_word ) {        /*        printf("\n--------------before delete------------------\n");        print_list_all_node( head );        printf("\n--------------------------------------------\n");        */        list_insert( tmp_word, root->count, tail, head, top_num );        /*        printf("\n--------------------after delete----------------------------\n");        print_list_all_node( head );        printf("\n-----------------------------------------------------------\n");        */    }    int i = 0;    for ( i; i < MAX_CHILD_NUM; i++ ) {        find_top_count1( root->next[i], tmp_word, tail, head, top_num );    }}void find_top_count(    trieTreeNode *root,    int top_num ){    if ( !root )        return;    int i = 0;    count_data *head = ( count_data * )malloc( sizeof(count_data) );    for ( i; i < MAX_CHILD_NUM; i++ ) {        char tmp_word[20] = {0};        find_top_count1( root->next[i], tmp_word, 0, head, top_num );    }    printf("出现次数最大前%d次的单词:\n", top_num);    count_data *p = head->next;    count_data *free_p = NULL;    while ( p != NULL ) {        free_p = p;        printf("前%d,count:%d\t%s\n", p->order, p->count, p->string);        p = p->next;        free( free_p );    }    free( head );}void tree_walk1(    trieTreeNode *root,    char *tmp_word,    int tail ){    if ( !root )        return;    tmp_word[tail] = root->letter;    tail++;    //printf("%c\n", root->letter);    if ( root->is_word ) {        int j = 0;        printf("count:%d\t", root->count);        for ( j; j < tail; j++ ) {            printf("%c", tmp_word[j]);        }        printf("\n");    }    int i = 0;    for ( i; i < MAX_CHILD_NUM; i++ ) {        tree_walk1( root->next[i], tmp_word, tail );    }}void tree_walk(    trieTreeNode *root ){    if ( !root )         return;    int i = 0;    for ( i; i < MAX_CHILD_NUM; i++ ) {        char tmp_word[20] = {0};        tree_walk1( root->next[i], tmp_word, 0 );    }}int main(    int argc,    char **argv ){    if ( argc != 3 ) {        PRINT("USAGE: please input words file & top number");        exit( 0 );    }    char *file_name = argv[1];    int top_num = atoi( argv[2] );    trieTree *tree = ( trieTree * )malloc( sizeof(trieTree) );    tree->root = create_node( -1 );    int fd = open(file_name, O_RDONLY);    if ( fd < 0 ) {        PRINT("OPEN FILE %s ERROR!!!(%s)", file_name, (char *)strerror(errno));        exit( 0 );    }    // 每次读取文件的缓冲区    char buf[1024 * 10] = {0};    // 每次读取的大小    int read_len = 1024;    // 读取的返回值    int read_bytes = 0;    // 从读取的缓冲区每次提取'\n' - '\n'之间的单词    char tmp_word[20] = {0};    // 读取文件缓冲区如果出现单词隔断，剩余部分在下一次    // read才能读到，这个index做单词继续拼接    int tmp_index = 0;    while ( 1 ) {        memset( buf, 0, read_len );        read_bytes = read( fd, buf, read_len );        if ( read_bytes <= 0 )            break;        //printf("readbytes:%d------\n%s\n", read_bytes, buf);        int cur = 0;        while ( cur < read_bytes ) {            // 单词文件最后一个单词末尾一定要有'\n'            if ( buf[cur] == '\n' ) {                tmp_word[tmp_index] = '\0';                //printf("insert word:%s\n", tmp_word);                insert( tree->root, tmp_word );                memset( tmp_word, 0, 20 );                tmp_index = 0;            } else {                tmp_word[tmp_index] = buf[cur];                tmp_index++;            }            cur++;        }    }    printf("\n========================================\n");    tree_walk( tree->root );    find_top_count( tree->root, top_num );    close( fd );    return 0;}

trie树的代码使用：./xxx word.txt 10即统计出现次数前10的单词，并打印单词和次数

例如对生成了10000个单词的word.txt文件，统计前5：
./xxx word.txt 5