最近了解es相关知识，发现term index是一棵trie树，于是参考网上blog，实现了一下trie数，发现这个数据结构非常实用。特记载于此。

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#include<iostream>
using namespace std;

#define SIZE 26

typedef struct trie_node
{
    int count;
    trie_node* childs[SIZE];
}* trie;

trie create()
{
    trie_node* node = new trie_node();
    node->count = 0;
    for(int i=0;i<SIZE;i++)
    {
         node->childs[i]=NULL;
    }
    return node;
}

void insert(trie root, char* k)
{
    trie_node* node = root;
    char* p = k;
    while(*p)
    {
        if(node->childs[*p-'a'] == NULL)
        {
            node->childs[*p-'a'] = create();
        }
        node = node->childs[*p-'a'];
        node->count +=1;
        ++p;
    }
    
}

int search(trie root, char* k)
{
    trie_node* node = root;
    char* p = k;
    while(*p && node!=NULL)
    {
        node = node->childs[*p-'a'];
        ++p;
    }
    if(node == NULL)
        return 0;
    else
        return node->count;
}

int main()
{
    char keys[][8]={"the", "a", "there", "answer", "any", "by", "bye", "their"};
    trie root = create();
    for(int i=0;i<8;i++)
        insert(root, keys[i]);

    printf("%s --- %d\n", "the", search(root, "the"));
    printf("%s --- %d\n", "these", search(root, "these"));
    printf("%s --- %d\n", "their", search(root, "their"));
    printf("%s --- %d\n", "thaw", search(root, "thaw"));
    printf("%s --- %d\n", "a", search(root, "a"));
    printf("%s --- %d\n", "b", search(root, "b")); 
    return 0;
}

参考

1 elasticsearch 倒排索引原理
2 Trie树（Prefix Tree）介绍这篇文章的代码貌似有点问题，看思路即可。