HDU2222 自动机（学习中）
题目大意：
给你很多个单词，然后给你一篇文章，问给出的单词在文章中出现的次数。
解题思路：
AC自动机入门题。需要注意的就是可能有重复单词
代码如下：
#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
using namespace std;
#define N 500010
char str[1000010], keyword[51];
int head, tail;
struct node
{
node *fail;
node *next[26];
int count;
node() //init
{
fail = NULL;
count = 0;
for(int i = 0; i < 26; ++i)
next[i] = NULL;
}
}*q[N];
node *root;
void insert(char *str) //建立Trie
{
int temp, len;
node *p = root;
len = strlen(str);
for(int i = 0; i < len; ++i)
{
temp = str[i] - 'a';
if(p->next[temp] == NULL)
p->next[temp] = new node();
p = p->next[temp];
}
p->count++;
}
void build_ac() //初始化fail指针，BFS
{
q[tail++] = root;
while(head != tail)
{
node *p = q[head++]; //弹出队头
node *temp = NULL;
for(int i = 0; i < 26; ++i)
{
if(p->next[i] != NULL)
{
if(p == root) //第一个元素fail必指向根
p->next[i]->fail = root;
else
{
temp = p->fail; //失败指针
while(temp != NULL) //2种情况结束：匹配为空or找到匹配
{
if(temp->next[i] != NULL) //找到匹配
{
p->next[i]->fail = temp->next[i];
break;
}
temp = temp->fail;
}
if(temp == NULL) //为空则从头匹配
p->next[i]->fail = root;
}
q[tail++] = p->next[i]; //入队
}
}
}
}
int query() //扫描
{
int index, len, result;
node *p = root; //Tire入口
result = 0;
len = strlen(str);
for(int i = 0; i < len; ++i)
{
index = str[i] - 'a';
while(p->next[index] == NULL && p != root) //跳转失败指针
p = p->fail;
p = p->next[index];
if(p == NULL)
p = root;
node *temp = p; //p不动，temp计算后缀串
while(temp != root && temp->count != -1)
{
result += temp->count;
temp->count = -1;
temp = temp->fail;
}
}
return result;
}
int main()
{
int ncase, num;
scanf("%d", &ncase);
while(ncase--)
{
head= tail = 0;
root = new node();
scanf("%d", &num);
getchar();
for(int i = 0; i < num; ++i)
{
gets(keyword);
insert(keyword);
}
build_ac();
scanf("%s", str);
printf("%d\n", query());
}
return 0;
}
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