字典树实例

字典树

 

又称单词查找树，Trie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。

一下是示例代码

#include <stdio.h>

#include <malloc.h>

#define MAX 26

typedef struct __trie{

    struct __trie* nodes[MAX];

    char c;

    char count;

    void* payload;

    struct __trie* parent;

}  Trie;

Trie* trie_new_node(void* payload)

{

    Trie* p = (Trie*)malloc(sizeof(Trie));

    if(NULL == p)

    {

        return NULL;

    }

    int i = 0;

    for(/* void */;i<MAX;i++)

    {

        p->nodes[i] = NULL;

    }

    p->c = 0;

    p->count = 0;

    p->payload = payload;

    p->parent = NULL;

    return p;

}

int trie_insert(Trie* t,char* str,void* payload)

{

    char c = *str;

    if(c == 0)

    {

        t->payload = payload;

        t->count = 1;

        return 0;

    }

    if(c > 'z' || c < 'a')

    {

        return -1;

    }

    int index = c - 'a';

    if(t->nodes[index] == NULL)

    {

        t->nodes[index] = trie_new_node(NULL);

        t->nodes[index]->c = c;

        t->nodes[index]->parent = t;

    }

    return trie_insert(t->nodes[index],++str,payload);

}

int trie_update(Trie* t,char* str,void* payload)

{

    return trie_insert(t,str,payload);

}

Trie* trie_find(Trie* t,char* str)

{

    if(*str == 0){

        if(t->count == 1)

        {

            return t;

        }

        return NULL;

    }

    int index = *str - 'a';

    if(t->nodes[index] ==  NULL)

    {

        return NULL;

    }

    return trie_find(t->nodes[index],++str);

}

void trie_delete(Trie* t,char* str){

    if(*str == 0){

        t->count = 0;

        return ;

    }

    int index = *str - 'a';

    Trie* node = t->nodes[index];

    if(node ==  NULL)

    {

        return ;

    }

    trie_delete(node,++str);

    int del = 1;

    int i;

    for(i=0;i<MAX;i++){

        if(node->nodes[i] != NULL){

            del = 0;

            break;

        }

    }

    if(del == 1 && node->count == 0){

        node->parent->nodes[node->c-'a'] = NULL;

        free(node);

    }

}

void trie_list(Trie* t,void(*handle)(void*)){

    if(t->count != 0){

        handle(t->payload);

    }

    int i=0;

    for(/*void*/;i<MAX;i++)

    {

        if(t->nodes[i] != NULL){

            printf("not empty\n");

            trie_list(t->nodes[i],handle);

        }

    }

}

int main(void)

{

    Trie* root = trie_new_node(NULL);

    trie_insert(root,"a","a\n");

    trie_insert(root,"abc","abc\n");

    trie_insert(root,"abcd","abcd\n");

    trie_list(root,printf);

    printf("\n\n\n\n\n");

    trie_delete(root,"abcd");

    trie_delete(root,"a");

    trie_list(root,printf);

    return 0;

}