trie字典树

Trie字典树

哈希的一个变种
原理类似于字典的查找 如一个集合里面有

"ab", "abc", "abd", "ca", "cd", "ef", "ha", "hai","hag" "hk"我要查找"hag"

   画图解题很肿要

  dictionary : { "ab", "abc", "abd", "ca", "cd", "ef", "ha", "hai","hag" "hk" }   trie_tree:                       root                      / |\ \                     a  c e h                    /  /| | |\                   b  a d f a k                  /|       /|                   c d      i g

定义结构：

struct trie{    struct trie *next[KIND];    int chldnum;      //number of child    char v;         // flag to judge whether it is complete                    //also the number of same string};

创建字典树：

void createTrie(const char *str){    int id = 0, len = 0, i;    struct trie *p, *q;    len = strlen(str);    p = root;    for ( i = 0; i < len; i++ )    {        id = str[i] - 'a';  //hash        if ( p->next[id] == NULL )        {        /*  first time  appear  */            q = (struct trie*)malloc(sizeof(struct trie));  //create child            memset(q, 0, sizeof(struct trie));            q->chldnum = 1;            p->next[id] = q;            p = p->next[id];    //go to child        }        else        {            p->next[id]->chldnum++;            p = p->next[id];  //go to child        }    }    p->v++;    return;}

查找：

int findTrie(char *str){    int id = 0, len = 0, i;    struct trie* p;    p = root;    len = strlen(str);    for ( i = 0; i < len; i++ )    {        id = str[i] - 'a';  //hash: id is hash address. str[i] is key.        if ( id < 0 || id >= KIND ) // deal with invalid input            return 0;        p = p->next[id];        if ( p == NULL )            return 0;       //str is not in the dictionary    }    if ( p->v > 0 )        return 1;  //dictionary has str    else        return 0;}

释放树

写到这里，我想说任何递归都可以写成非递归的形式，

因为递归返回时，在栈里面保存了返回的地址；同理，如果我们定义一个带父结点的链表，就可以实现非递归了

int dealwithTrie(struct trie* T){    int i;    if ( T == NULL )        return 0;    for ( i = 0; i < KIND; i++ )    {        if ( T->next[i] != NULL )            dealwithTrie(T->next[i]);    }    free(T);    T = NULL;    return 0;}

完整代码：

#include <stdio.h>#include <string.h>#include <stdlib.h>#define KIND    26#define MAX     10#define MAXSTR  32struct trie{    struct trie *next[KIND];    int chldnum;      //number of child    char v;         // flag to judge whether it is complete                    //also the number of same string};struct trie *root;void createTrie(const char *str){    int id = 0, len = 0, i;    struct trie *p, *q;    len = strlen(str);    p = root;    for ( i = 0; i < len; i++ )    {        id = str[i] - 'a';  //hash        if ( p->next[id] == NULL )        {        /*  first time  appear  */            q = (struct trie*)malloc(sizeof(struct trie));  //create child            memset(q, 0, sizeof(struct trie));            q->chldnum = 1;            p->next[id] = q;            p = p->next[id];    //go to child        }        else        {            p->next[id]->chldnum++;            p = p->next[id];  //go to child        }    }    p->v++;    return;}int findTrie(char *str){    int id = 0, len = 0, i;    struct trie* p;    p = root;    len = strlen(str);    for ( i = 0; i < len; i++ )    {        id = str[i] - 'a';  //hash: id is hash address. str[i] is key.        if ( id < 0 || id >= KIND ) // deal with invalid input            return 0;        p = p->next[id];        if ( p == NULL )            return 0;       //str is not in the dictionary    }    if ( p->v > 0 )        return 1;  //dictionary has str    else        return 0;}int dealwithTrie(struct trie* T){    int i;    if ( T == NULL )        return 0;    for ( i = 0; i < KIND; i++ )    {        if ( T->next[i] != NULL )            dealwithTrie(T->next[i]);    }    free(T);    T = NULL;    return 0;}/*  dictionary : { "ab", "abc", "abd", "ca", "cd", "ef", "ha", "hai","hag" "hk" }*   trie_tree:*                       root*                      / |\ \*                     a  c e h*                    /  /| | |\*                   b  a d f a k*                  /|       /|  *                 c d      i g*/int main(){    int i;    char buffer[MAXSTR];    char *dictionary[MAX] = {"ca",                            "cd",                            "abc",                            "ab",                            "abd",                            "ef",                            "ha",                            "hai",                            "hag",                            "hk"                            };    root = (struct trie*)malloc(sizeof(struct trie));    memset(root, 0, sizeof(struct trie));    printf("#system start,init trie tree\n");    for ( i = 0; i < MAX; i++ )    {        createTrie(dictionary[i]);    }    sleep(1);    while ( buffer[0] != 'q' ) {        memset(buffer, 0, MAXSTR);        printf("#");        scanf("%s", buffer);        printf("************finding**********\n");        sleep(2);        if ( findTrie(buffer) )            printf("#Result:%s is in the dictionary!\n", buffer);        else            printf("#Result:%s is not in the dictionary!\n", buffer);    }            dealwithTrie(root);    return 0;}