Trie tree（字典树）

　　Trie tree有时被称为（digital tree）或（radix tree or prefix tree）。

　　可能是编译器问题，我的实现方法用gcc编译器，debug没问题，但一run就有问题。。。

　　Debug output:

Starting debugger: C:TDM-GCC-64ingdb.exe -nx -fullname -quiet  -args E:/CodeBlocks_C++Projects/NYOJ/bin/Debug/NYOJ.exe
done
Setting breakpoints
Debugger name and version: GNU gdb (GDB) 7.9.1
Child process PID: 208
[Inferior 1 (process 208) exited normally]
Debugger finished with status 0

　　弄了很久，还以为是我哪里指针处理没做好，但最后不管怎么想都觉得逻辑都没问题，于是换VS，run成功了，而且结果是正确的。

　　原理其实挺简单的，个人认为只用一下看wiki上的图就能够明白什么是前缀树以及如何设计这样的数据结构了。遍历的思路用的是二叉树的后序遍历思想-DFS。ps:其实成员letter没有必要有。。。

　　code：

#include "stdafx.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE 26
#define INDEX(c) ((c) - 'a')
#define ARR_SIZE(strs) (sizeof((strs))/sizeof(strs[0]))

typedef struct BaseNode {
	struct BaseNode* children[SIZE];
	char letter;
	const char*s;
}trie;

trie*initialized()
{
	trie*root = (trie*)malloc(sizeof(trie));
	root->letter = 0;
	for (int i = 0; i < SIZE; i++) root->children[i] = NULL;
	root->s = NULL;
	return root;
}

trie*insert(trie*root, const char str[])
{
	trie*node = root;
	int i, j;
	for (i = 0; str[i] != ''; i++)
	{
		if (node->children[INDEX(str[i])] == NULL)
		{
			trie*curr = (trie*)malloc(sizeof(trie));
			curr->letter = str[i];
			for (j = 0; j < SIZE; j++) curr->children[j] = NULL;
			curr->s = NULL;
			if (i + 1 == (int)strlen(str))
				curr->s = str;
			node->children[INDEX(str[i])] = curr;
		}
		node = node->children[INDEX(str[i])];
	}

	return root;
}

trie*search(trie*root, const char str[])
{
	trie*node = root;
	for (int i = 0; i < (int)strlen(str); i++)
	{
		if (node != NULL)
		{
			node = node->children[INDEX(str[i])];
			// printf("%c -> ", node->letter);
		}
		else
			break;
	}
	return node;
}

bool remove_helper(trie*node)
{
	for (int i = 0; i < SIZE; i++)
	{
		if (node->children[i] != NULL)
			return true;
	}
	return false;
}

void remove(trie**node, const char*str)
{
	if (*node != NULL)
	{
		char c = *str;
		++str;
		remove(&(*node)->children[INDEX(c)], str);
		if (!remove_helper(*node))
		{
			free(*node);
			*node = NULL;
		}
	}
}

void show(trie*node)
{
	if (node != NULL)
	{
		for (int i = 0; i < SIZE; i++)
		{
			show(node->children[i]);
		}
		printf("%s
", node->s ? node->s : "");
	}
}

void destory(trie**node)
{
	if (*node != NULL)
	{
		for (int i = 0; i < SIZE; i++)
		{
			destory(&(*node)->children[i]);
		}
		free(*node);
		*node = NULL;
	}
}

int main()
{
	char strs[][12] = { "tea","eat","engineer","table","profile" };
	trie*root;

	root = initialized();

	for (int i = 0; i < (int)ARR_SIZE(strs); i++)
	{
		root = insert(root, strs[i]);
	}

	show(root);
	remove(&root, "tea");
	// trie*node = search(root, "engineer");
	show(root);
	destory(&root);
	getchar();
	return 0;
}

　　Output:

eat
engineer
profile
table
tea

eat
engineer
profile
table

　　参考：

　　　　https://github.com/darkchii/cosmos/blob/master/code/data_structures/src/tree/tree/trie/trie.c

　　　　https://en.wikipedia.org/wiki/Trie