POJ：3461-Oulipo（KMP模板题）

原题传送：http://poj.org/problem?id=3461

Oulipo

Time Limit: 1000MS Memory Limit: 65536K

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

Sample Output

1
3
0

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之前看KMP算法，看了几次都没看懂，现在搞懂了一些，写了一个模板题试试水。

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#include<stdio.h>#include<string>#include<cstring>#include<iostream>using namespace std;const int maxn = 1e4+100;char s1[maxn],s2[1000100];int next[maxn];void cal_next()//获得next数组{    int k;    k = next[0] = -1;    int len = strlen(s1);    for(int i=1;i<len;i++)    {        while(k>-1 && s1[i] != s1[k+1])            k = next[k];        if(s1[i] == s1[k+1])            k++;        next[i] = k;    }}int KMP(){    int ans = 0;    int len = strlen(s2);    int k = -1;    int len1 = strlen(s1);    for(int i=0;i<len;i++)    {        while(k>-1 && s1[k+1] != s2[i])            k = next[k];        if(s1[k+1] == s2[i])            k++;        if(k == len1-1)        {            ans++;            k = next[k];        }    }    return ans;}int main(){    int t;    scanf("%d",&t);    while(t--)    {        scanf("%s%s",s1,s2);        cal_next();        int ans = KMP();        printf("%d\n",ans);    }    return 0;}