HDU 3336 Count the string【KMP】

题目：

The French author Georges Perec (1936–1982) once wrote a book, La disparition, without the letter 'e'. He was a member of the Oulipo group. A quote from the book: 

Tout avait Pair normal, mais tout s’affirmait faux. Tout avait Fair normal, d’abord, puis surgissait l’inhumain, l’affolant. Il aurait voulu savoir où s’articulait l’association qui l’unissait au roman : stir son tapis, assaillant à tout instant son imagination, l’intuition d’un tabou, la vision d’un mal obscur, d’un quoi vacant, d’un non-dit : la vision, l’avision d’un oubli commandant tout, où s’abolissait la raison : tout avait l’air normal mais… 

Perec would probably have scored high (or rather, low) in the following contest. People are asked to write a perhaps even meaningful text on some subject with as few occurrences of a given “word” as possible. Our task is to provide the jury with a program that counts these occurrences, in order to obtain a ranking of the competitors. These competitors often write very long texts with nonsense meaning; a sequence of 500,000 consecutive 'T's is not unusual. And they never use spaces. 

So we want to quickly find out how often a word, i.e., a given string, occurs in a text. More formally: given the alphabet {'A', 'B', 'C', …, 'Z'} and two finite strings over that alphabet, a word W and a text T, count the number of occurrences of W in T. All the consecutive characters of W must exactly match consecutive characters of T. Occurrences may overlap. 
 

Input

The first line of the input file contains a single number: the number of test cases to follow. Each test case has the following format: 

One line with the word W, a string over {'A', 'B', 'C', …, 'Z'}, with 1 ≤ |W| ≤ 10,000 (here |W| denotes the length of the string W). 
One line with the text T, a string over {'A', 'B', 'C', …, 'Z'}, with |W| ≤ |T| ≤ 1,000,000. 

Output

For every test case in the input file, the output should contain a single number, on a single line: the number of occurrences of the word W in the text T. 
 

Sample Input

3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

Sample Output

1
3
0

题目大意：

       查找字符串 A 在字符串 B 中出现了几次；

解题思路;

       KMP模板题；

实现代码：

#include<cstdio>
#include<fstream>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<string>
#include<cstring>
#include<string.h>
#include<queue>
#include<vector>
#include<map>
using namespace std;
int Next[1000005];

void getnext(string ss,int d){
    int k=-1;   Next[0]=-1;
    for(int i=1;i<d;i++){
        while(k>-1&&ss[k+1]!=ss[i])
            k=Next[k];
        if(ss[k+1]==ss[i]) k++;
        Next[i]=k;
    }
}
int  kmp(string s1,int d1,string s2,int d2){   //判断母串中是否存在子串
    int k=-1,ans=0;
    for(int i=0;i<d1;i++){
        while(k>-1&&s2[k+1]!=s1[i])
            k=Next[k];
        if(s2[k+1]==s1[i])k++;
        if(k==d2-1)ans++;
    }
    return ans;
}
int main(){
    ios::sync_with_stdio(false);    //加速
    cin.tie(0);
    int t,n;
    cin>>t;
    while(t--){
        string op,s;
        cin>>op;       //每组数据有n个字符串
        cin>>s;
        getnext(op,op.size());
        int ans=kmp(s,s.size(),op,op.size());
        cout<<ans<<endl;
    }
    return 0;
}