AC自动机妙用

理解题意之后，很自然的想到了用AC自动机搞，结果网上一搜，全是暴搜，按照自己的思想，AC自动机搞起，果然在提交了数次之后，看到了Accept。

AC自动机需要三个步骤：

第一步：建立字典树；

第二步：为字典树建立 Fail 指针 ；

第三步：进行匹配；

#include<iostream>
#include<string>
#include<string.h>
#include<cctype>
#include<queue>
#include<stdio.h>

#define max(x,y) ((x) > (y) ? (x) : (y))

using namespace std ;

struct Node	{
	Node *next[26] ; 
	Node *fail ;
	bool is_over ;
	int len ;
};

Node* new_node()	{
	Node *root = new Node ;
	root ->fail = NULL ;
	for(int i = 0 ; i< 26 ; i++)
		root->next[i] = NULL ;
	root ->is_over = false ;
	return root ;
}

void build_tree( Node *root , char *s )	{
	int len = strlen(s) ;
	for(int i = 0 ; i < len ; i++)	{
		if(root->next[s[i] - 'a'] == NULL)
			root->next[s[i] - 'a'] = new_node() ;
		root = root ->next[s[i] - 'a'] ;
	}
	root ->is_over = true ;
	root ->len = len ;
}

void build_fail(Node *root)	{
	Node *r = root ;
	queue< Node* > q ;
	q.push(root) ;
	while(!q.empty())	{
		r = q.front() ;
		q.pop() ;
		Node *p = r ;
		for(int i = 0 ; i < 26 ; i++)	{
			if(p->next[i] != NULL)	{
				if(p == root)	{
					p->next[i]->fail = root ;
					q.push(p->next[i]) ;
					continue ;
				}
				while(r->fail->next[i] == NULL && r ->fail != root)
					r = r->fail ;
				if(r->fail ->next[i] != NULL)
					p ->next[i]->fail = r ->fail ->next[i] ;
				else
					p ->next[i] ->fail = root ;
				q.push(p->next[i]) ;
			}
		}
	}
}

int A_C(Node *root , char *s)	{
	int len = strlen(s) ;
	Node *r = root ;
	int count = 0 ;
	for(int i = 0 ; i < len ; i++)	{
		if(!isalpha(s[i]))
			continue ;
		if(r->next[s[i]-'a'] != NULL)	{
			r = r ->next[s[i]-'a'] ;
			if(r->is_over && !(islower(s[i+1])) && !(islower(s[i - r->len])) )	
				count++ ;
		}
		else {
			while(r->next[s[i]-'a'] == NULL && r != root )
				r = r ->fail ;
			if(r ->next[s[i] - 'a'] != NULL)
				r = r ->next[s[i] - 'a'] ;
			else
				r = root ;
			if(r->is_over && (!(isalpha(s[i+1])) ) && !(islower(s[i - r->len])) 	)	
				count++ ;	
		}
	}
	
	return count ;
}


int main()	{
	int n , m ; 
	int t = 1 ;
	while(scanf("%d%d",&n,&m) == 2)	{
		Node *root = new_node() ;
		Node *r = root ;
		while(n--)	{
			char s[30] ;
			scanf("%s",&s) ;
			getchar() ;
			build_tree(root,s) ;
			root = r ;
		}
		r->fail = NULL ;
		root = r ;
		build_fail(r) ;
		char str[30][100] ;
		char str1[30][100] ;
		int count[30] = {0} ;
		int ma = 0 ;
		for(int i = 0 ; i < m ; i++)	{
			gets(str[i]) ;
			strcpy(str1[i],str[i]) ;
			int len = strlen(str[i]) ;
			for(int j = 0 ; j < len ; j++)
				if(isupper(str[i][j]))
					str[i][j] += 32 ;
			count[i] = A_C(root,str[i]) ;
			ma = max(ma,count[i]) ;
		}
		cout << "Excuse Set #" << t++ << endl;
		for(int k = 0 ; k < m ; k++)
			if(count[k] == ma)	
				cout << str1[k] << endl ;
			cout << endl ;
	}
	return 0 ;
}