【POJ3461】Oulipo

题面

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

题解

这是一道KMP模板题
我竟然Wa了N遍才AC（实测N=4）

题目大意：给你T组字符串，问第一个串在第二个中出现了几次

KMP太毒了，，，，老是写Wa。。。。
滑稽
这一道题用来复习KMP

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
#define Next nt
char a[1000100],b[1000100];
int nt[1000100];
inline void getnext()//获得字符串s的next数组
{
    int l=strlen(a),t;
    Next[0]=-1;//如果在0位置失配则是向下移动一位
    for(int i=1;i<l;++i)//依次求解后面的next数组
    {
        t=Next[i-1];
        while(a[t+1]!=a[i]&&t>=0)
            t=Next[t];
        if(a[t+1]==a[i])
            Next[i]=t+1;
        else
            Next[i]=-1;
    }
}
int KMP()
{
	   int l=strlen(b);
	   int l2=strlen(a); 
	   int i=0,j=0;//匹配指针 
	   int sum=0;
	   while(i<l)
	   {
	   	       if(a[j]==b[i])
	   	       {
	   	       	     j++;i++;
	   	       	     if(j==l2)//匹配完了
					 {
					 	    ++sum;
					 	    j=nt[j-1]+1;
					 }
	   	       }
	   	       else//失配 
	   	       {
	   	       	     if(j==0)//首位失配
						   i++;
					 else//跳转 
					    j=nt[j-1]+1; 
	   	       }
	   }
	   return sum;
}
int main()
{
	int T;
	cin>>T;
	while(T--)
	{
    	scanf("%s",a);
    	scanf("%s",b);
    	//memset(nt,0,sizeof(nt));
    	getnext();
    	cout<<KMP()<<endl;
    }
    return 0;
    
}