poj 3461 Oulipo（KMP）

Description

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

S
4000
ample Output

1

3

0

ps：KMP模板题

代码：

#include<stdio.h>
#include<string.h>

const int maxn=1000010;
const int maxv=10010;
char w[maxv],p[maxn];
int nxt[maxv];

void get_next()
{
int len=strlen(w);
for(int q=0,i=1;i<len;++i)
{
while(q&&w[q]!=w[i])
q=nxt[q];
if(w[q]==w[i])
++q;
nxt[i+1]=q;
}
}

int kmp()
{
get_next();
int len_w=strlen(w);
int len_p=strlen(p);
int ans=0;
for(int q=0,i=0;i<len_p;++i)
{
while(q&&w[q]!=p[i])
q=nxt[q];
if(w[q]==p[i])
++q;
if(q==len_w)
++ans;
}
return ans;
}

int main()
{
int t;
scanf("%d",&t);
while(t--)
{
scanf("%s %s",w,p);
printf("%d\n",kmp());
}
return 0;
}

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