KMP算法 学习例题 POJ 3461Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 37971		Accepted: 15286

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

Source

BAPC 2006 Qualification

题目大意：T组数据，每组数据先输入子串后输入母串，对于每一组数据输出子串在母串中出现了多少次~

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
int next[100010];
char p[10010],s[1000010];
int t,num,l1,l2;
void getnext(){
    int j=0,k=-1;
    next[0]=-1;
    while(j<l2){
        if(k==-1||p[j]==p[k]){ j++;k++;next[j]=k; }
        else k=next[k];
    }
}
int KMP(){
    int num(0),i=0,j=0;
    getnext();
    while(i<l1){
        if(j==-1||s[i]==p[j]){ i++;j++; }
        else j=next[j];
        if(j==l2) { num++;j=next[j]; }
    }
    return num;
}
int main()
{
    scanf("%d",&t);
    while(t--){
        scanf("%s%s",p,s);
        l1=strlen(s);l2=strlen(p);
        printf("%d\n",KMP());
    }
    return 0;
}

注意这个题目的输入顺序，是先输入字串后母串，刚开始被坑了~