HDU 2222 Keywords Search AC自己主动机入门题

单词统计的题目，给出一些单词，统计有多少单词在一个文本中出现，最经典的入门题了。

AC自己主动机的基础：

1 Trie。 以这个数据结构为基础的，只是添加一个fail指针和构造fail的函数

2 KMP，不是直接运用KMP。而是须要KMP的思想。KMP思想都没有的话，理解这个算法会更加吃力的。

注意本题的单词会有反复出现的，一个单词仅仅能统计一次。

搜索了一下网上的题解。发现好多代码都是一大抄的啊。⊙﹏⊙b汗。

本博客的乃是原创代码。代码风格也是几乎相同固定的，转载请注明出处：http://blog.csdn.net/kenden23。不少所谓的IT站点转载我的文章，不但链接没给出，连作者也没有，还好意思说自己是IT站点吗？

请尊重作者。假设觉得这些算法代码那么好敲的，能够自己去敲去。

#include <cstdio>

const int ARR_SIZE = 26;
const int MAX_N = 10001;
const int MAX_M = 1000001;
const int MAX_KEY_LEN = 51;

struct Node
{
Node *arr[ARR_SIZE];
Node *fail;
int n;
};

void clearNode(Node *rt)
{
for (int i = 0; i < ARR_SIZE; i++)
{
rt->arr[i] = NULL;
}
rt->n = 0;
rt->fail = NULL;
}

Node *q[MAX_KEY_LEN*MAX_N], pool[MAX_KEY_LEN*MAX_N], *Trie;
int head, tail, poolID;

void insert(char *str)
{
Node *pCrawl = Trie;
for ( ; *str; str++)
{
int id = *str - 'a';
if (!pCrawl->arr[id])
{
pCrawl->arr[id] = &pool[poolID++];
clearNode(pCrawl->arr[id]);
}
pCrawl = pCrawl->arr[id];
}
pCrawl->n++;
}

void buildFail()
{
Node *pCrawl;
head = tail = 0;
q[tail++] = Trie;
while (head < tail)
{
pCrawl = q[head++];
for (int i = 0; i < ARR_SIZE; i++)
{
if (pCrawl->arr[i] == NULL) continue;
pCrawl->arr[i]->fail = Trie;//initialize all to Trie
Node *fail = pCrawl->fail;
while (fail)
{
if (fail->arr[i])//find the first next up level match
{//which make it the longest match and the best.
pCrawl->arr[i]->fail = fail->arr[i];
break;
}
fail = fail->fail;
}//whi (p != NULL)
q[tail++] = pCrawl->arr[i];
}//for (int i = 0; i < kind; i++)
}//while (head < tail)
}

int searchWordsInText(char *text)
{
Node *pCrawl = Trie;
int i = 0, ans = 0;
while (text[i])
{
int id = text[i++] - 'a';
//find the longest prefix match
while (!pCrawl->arr[id] && pCrawl != Trie) pCrawl = pCrawl->fail;
if (pCrawl->arr[id]) pCrawl = pCrawl->arr[id];
else continue;

Node *tmp = pCrawl;
while (tmp && tmp->n != -1)
{//If one word apprear multiply times, only count as one time.
ans += tmp->n;
tmp->n = -1;
tmp = tmp->fail;
}//traval through all words that end with text[i], add them to result
}
return ans;
}

int main()
{
int T, n;
char keyWord[MAX_KEY_LEN], text[MAX_M];
scanf("%d", &T);
while (T--)
{
Trie = &pool[0];
clearNode(Trie);
poolID = 1;

scanf("%d", &n);
getchar();
while (n--)
{
gets(keyWord);
insert(keyWord);
}
gets(text);
buildFail();
printf("%d\n", searchWordsInText(text));
}
return 0;
}