Oulipo（kmp）

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

题意： 一次给两个字符串，先给模式串，再给主串，问在主串中能找到几个模式串（可重叠）

思路： kmp模板

AC代码：

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
const int N=1e6+100;
char s[N],t[N];//s主，t模式
int tt,sl,tl,ne[N];
void getnext()
{ne[0]=-1;//下标为0的字符前没有字符串，单独处理，赋为-1 int i=0,j=-1;while(i<tl){if(j==-1||t[i]==t[j]){i++;j++;//对应字符匹配，i，j同步向后移 ne[i]=j;//赋值 }else//不匹配 ，i不变，j回溯j=ne[j];}
}
int kmp()
{int i,j=0,sum=0;//j=0初始化在模式串的第一个位置 for(i=0;i<sl;i++)//遍历整个主串 {while(j&&s[i]!=t[j])//顺着不匹配的边走，直到能匹配，最坏的情况j=0 j=ne[j];if(s[i]==t[j])//匹配成功，下一个位置 j++;if(j==tl)//在主串中找到了模式串 {sum++;//总数+1 j=ne[j];//下一个位置 //若不可重叠，j=0;}}return sum;
}
int main()
{scanf("%d",&tt);while(tt--){memset(ne,0,sizeof(ne));scanf("%s",t);scanf("%s",s);sl=strlen(s);tl=strlen(t);getnext();printf("%d\n",kmp());}return 0;}

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