AC自动机算法

AC自动机算法在1975年产生于贝尔实验室，是著名的多模匹配算法之一，由Alfred V.Aho发明，他还是编译原理红龙书的作者之一。

AC自动机算法是字典树和KMP算法的结合，主要用于多字符串匹配，比如给定若干个单词，再给定一篇文章，问在文章中出现了多少个单词。AC自动机算法可以快速解决此类问题。

 

例题:hdu 2222

Keywords Search

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 18971    Accepted Submission(s): 6329

Problem Description

In the modern time, Search engine came into the life of everybody like Google, Baidu, etc.
Wiskey also wants to bring this feature to his image retrieval system.
Every image have a long description, when users type some keywords to find the image, the system will match the keywords with description of image and show the image which the most keywords be matched.
To simplify the problem, giving you a description of image, and some keywords, you should tell me how many keywords will be match.

 

Input

First line will contain one integer means how many cases will follow by.
Each case will contain two integers N means the number of keywords and N keywords follow. (N <= 10000)
Each keyword will only contains characters 'a'-'z', and the length will be not longer than 50.
The last line is the description, and the length will be not longer than 1000000.

 

Output

Print how many keywords are contained in the description.

 

Sample Input

   
   
   
   

    
    
    
    1
5
she
he
say
shr
her
yasherhs
   
   
   
   

 

 

Sample Output

   
   
   
   

    
    
    
    3
   
   
   
   

 

#include <stdio.h>
#include <memory.h>
#include <iostream>
using namespace std;

//字典树结点
struct TRIE_TREE_NODE
{
	TRIE_TREE_NODE *child[26];
	int count;
	TRIE_TREE_NODE *fail;	//失败指针
};

TRIE_TREE_NODE *ROOT;

//初始化一个字典树结点
void init_trie_tree_node(TRIE_TREE_NODE *node)
{
	memset(node->child ,NULL ,26*4);
	node->count = 0;
	node->fail = NULL;
}

void insert_into_trie_tree(TRIE_TREE_NODE *node ,char *str)
{
	int i;
	unsigned char ch;
	for(i = 0 ; '\0' != str[i] ;i ++)
	{
		ch = str[i]-'a';
		if(NULL == node->child[ch])
		{
			node->child[ch] = (TRIE_TREE_NODE*)malloc(sizeof(TRIE_TREE_NODE));
			init_trie_tree_node(node->child[ch]);
		}
		node = node->child[ch];
	}
	node->count ++;
}


TRIE_TREE_NODE *queue[1000000];

//构造一颗字典树每个结点的失败指针
void build_fail_pointer(TRIE_TREE_NODE *root)
{
	int head ,rear ,i;
	TRIE_TREE_NODE *cur_node ,*t;

	root->fail = root;
	head = rear = 0;
	queue[rear++] = root;

	while(head < rear)
	{
		cur_node = queue[head++];
		for(i = 0 ; i < 26 ;i ++)
		{
			if(NULL != cur_node->child[i])
			{
				if(root == cur_node)
					cur_node->child[i]->fail = root;
				else
				{
					t = cur_node->fail;
					while(root != t && NULL == t->child[i])
						t = t->fail;
					if(NULL != t->child[i])
						t = t->child[i];
					cur_node->child[i]->fail = t;
				}
				queue[rear++] = cur_node->child[i];
			}
		}
	}
}


int search(TRIE_TREE_NODE *root ,char *str)
{
	int count = 0 ,i;
	unsigned char ch;
	TRIE_TREE_NODE *cur_node = root ,*t;

	for(i = 0 ; '\0' != str[i] ;i ++)
	{
		ch = str[i]-'a';
		while(NULL == cur_node->child[ch] && cur_node != root)
			cur_node = cur_node->fail;
		if(cur_node->child[ch] != NULL )
			cur_node = cur_node->child[ch];

		t = cur_node;
		while(root != t && t->count != -1)
		{
			count += t->count;
			t->count = -1;
			t = t->fail;
		}
	}
	return count;
}

char str[1000100];


void  release_trie_tree(TRIE_TREE_NODE *root)
{
	int i;
	for(i = 0 ;i < 26 ;i ++)
	{
		if(NULL != root->child[i])
			release_trie_tree(root->child[i]);
	}
	free(root);
}

int main()
{
	int t ,n ,i;
	cin >> t;
	while(t--)
	{
		ROOT = (TRIE_TREE_NODE*)malloc(sizeof(TRIE_TREE_NODE));
		init_trie_tree_node(ROOT);

		cin >> n;
		for(i = 0 ;i < n ;i ++)
		{
			scanf("%s" ,str);
			insert_into_trie_tree(ROOT ,str );
		}

		build_fail_pointer(ROOT);

		scanf("%s" ,str);
		cout<<search(ROOT ,str)<<endl;
		release_trie_tree(ROOT);
	}
	return 0;
}