Trie树

字典树用于单词统计，查询，非常有用。现在就Trie树给出C语言实现。

#include <stdio.h>
#include <malloc.h>

#define MAXN  26

struct Trie{
    int count;   //单词计数
    int flag;    // 1表示是单词，0表示不是单词
    struct Trie *next[MAXN];
};

struct Trie *rt;

//初始化Trie树
void trie_init(){
    int i;
    rt = (struct Trie*)malloc(sizeof(struct Trie));

    rt->count = 0;
    rt->flag = 0;
    for(i=0; i<MAXN; ++i)
        rt->next[i] = NULL;
}

//插入单词
void trie_insert(char *s){
    int i;
    struct Trie *tmp = rt;

    for(s; *s!='\0'; ++s){
        if(tmp->next[*s -'a'] == NULL){
             struct Trie *cur = (struct Trie*)malloc(sizeof(struct Trie));
             cur->count = 0;
             cur->flag = 0;
             for(i=0; i<MAXN; ++i)
                 cur->next[i] = NULL;
             tmp->next[*s -'a'] = cur;
        }
        tmp->count++;
        tmp = tmp->next[*s -'a'];
    }
    tmp->flag = 1;
    tmp->count++;
}

//查询给定字符串前缀的单词数目
int trie_search(char *s){

    struct Trie *tmp = rt;
    for(s; *s!='\0'; ++s){
        if(tmp->next[*s -'a'] == NULL)
            return 0;
        tmp = tmp->next[*s -'a'];
    }
    return tmp->count;
}

//删除整个Trie树
void trie_del(struct Trie *root){
    int i;
    for(i=0; i<MAXN; ++i){
       if(root->next[i] != NULL)
        trie_del(root->next[i]);
    }
    free(root);
}

int main(){
    int i, n, m;
    char ch[15];

    FILE *fin;
    fin = fopen("input.txt", "r");

    while(fscanf(fin, "%d", &n) != EOF){
       trie_init();
       for(i=0; i<n; ++i){
           fscanf(fin, "%s", ch);         
           trie_insert(ch);
       }
       fscanf(fin, "%d", &m);
       for(i=0; i<m; ++i){
           fscanf(fin, "%s", ch);
           printf("%d\n", trie_search(ch));
       }
       trie_del(rt);
    }  

    return 0;
}