hdu 6096---String(AC自动机)

题目链接

 

Problem Description
Bob has a dictionary with N words in it.
Now there is a list of words in which the middle part of the word has continuous letters disappeared. The middle part does not include the first and last character.
We only know the prefix and suffix of each word, and the number of characters missing is uncertain, it could be 0. But the prefix and suffix of each word can not overlap.
For each word in the list, Bob wants to determine which word is in the dictionary by prefix and suffix.
There are probably many answers. You just have to figure out how many words may be the answer.
 

 

Input
The first line of the input gives the number of test cases T; T test cases follow.
Each test case contains two integer N and Q, The number of words in the dictionary, and the number of words in the list.
Next N line, each line has a string Wi, represents the ith word in the dictionary (0<|Wi|100000)
Next Q line, each line has two string Pi , Si, represents the prefix and suffix of the ith word in the list (0<|Pi|,|Si|100000,0<|Pi|+|Si|100000)
All of the above characters are lowercase letters.
The dictionary does not contain the same words.

Limits
T5
0<N,Q100000
Si+Pi500000
Wi500000
 

 

Output
For each test case, output Q lines, an integer per line, represents the answer to each word in the list.
 

 

Sample Input
1
4 4
aba
cde
acdefa
cdef
a a
cd ef
ac a
ce f
 

 

Sample Output
2
1
1
0
 
 
题意:有 n 个由小写字母构成的串,现在有q次询问,每次给一个前缀和后缀,求这n个串中有多少个串满足给的前缀和后缀,前缀和后缀不能在这个字符串中重叠?
 
思路:对于给的n个串s[i],修改为 s[i] = s[i] + "_" + s[i] ,对于每次询问输入的前缀pre和后缀suf,修改为str=suf+"_"+pre,对这q次询问的前缀后缀构成的串 构建tire树,然后用AC自动机匹配跑一下即可。但是这样会存在冗余,例如:aaa,前缀aa 后缀aa,那么也会匹配上,所以比较时还得判断一下长度。
 
代码如下:
#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <string>
#include <queue>
#include <vector>
using namespace std;
const int N=1e5+5;
string s[N];
struct Node{
    Node *son[30];
    Node *fail;
    int flag;
    int len;
}tr[6*N];
Node *root;
queue<Node*>Q;
int ans[N];
vector<int>v[N];
int tot;

void init()
{
    tot=0;
    memset(ans,0,sizeof(ans));
    root=&tr[0];
    while(!Q.empty()) Q.pop();
    for(int i=0;i<N;i++) v[i].clear();
    for(int i=0;i<6*N;i++)
    {
        tr[i].flag=0;
        tr[i].fail=NULL;
        for(int j=0;j<30;j++) tr[i].son[j]=NULL;
    }
}
void build(string s,int id)
{
    Node *now=root;
    for(int i=0;i<s.length();i++)
    {
       int x=s[i]-'_';
       if(!now->son[x]) now->son[x]=&tr[++tot];
       now=now->son[x];
    }
    if(now->flag) {
        v[now->flag].push_back(id);
        return ;
    }
    now->flag=id;
    now->len=s.length();
}
void setFail()
{
    Q.push(root);
    while(!Q.empty())
    {
        Node *now=Q.front(); Q.pop();
        for(int i=0;i<30;i++)
        {
            if(now->son[i])
            {
                Node *p=now->fail;
                while(p && (!(p->son[i]))) p=p->fail;
                now->son[i]->fail=(p)?p->son[i]:root;
                Q.push(now->son[i]);
            }
            else now->son[i]=(now!=root)?now->fail->son[i]:root;
        }
    }
}
void query(string s)
{
    Node *now=root;
    int len=s.length();
    for(int i=0;i<len;i++)
    {
        int x=s[i]-'_';
        now=now->son[x];
        Node *p=now;
        while(p!=root)
        {
            if(p->flag && p->len<=len/2+1) ans[p->flag]++;
            p=p->fail;
        }
    }
}
int main()
{
    int T; cin>>T;
    while(T--)
    {
        init();
        int n,q; scanf("%d%d",&n,&q);
        for(int i=1;i<=n;i++)
        {
            cin>>s[i];
            s[i]=s[i]+"_"+s[i];
        }
        for(int i=1;i<=q;i++)
        {
            string s1,s2; cin>>s1>>s2;
            string ss=s2+"_"+s1;
            build(ss,i);
        }
        setFail();
        for(int i=1;i<=n;i++)
        {
            query(s[i]);
        }
        for(int i=1;i<=q;i++)  ///处理相同的前后缀;
        {
            for(int j=0;j<v[i].size();j++)
                ans[v[i][j]]=ans[i];
        }
        for(int i=1;i<=q;i++) printf("%d\n",ans[i]);
    }
    return 0;
}

 

posted @ 2017-09-02 14:15 茶飘香~ 阅读(...) 评论(...) 编辑 收藏