HDU1686 Oulipo

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本文介绍了一个基于KMP算法的比赛题目，详细解释了如何通过KMP算法解决字符串匹配问题，包括获取next数组和进行KMP匹配的过程。

Oulipo

Time Limit: 3000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 15910 Accepted Submission(s): 6321

Problem 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

华东区大学生程序设计邀请赛_热身赛

题目的意思是每次查询问一个字符串在另一个中出现的次数

思路：KMP匹配

#include<bits/stdc++.h>

using namespace std;

char a[1000009],b[10009];
int nt[10009];
int n,m;

void get_next()
{
    nt[0]=-1;
     m=strlen(b);
    for(int i=0; i<m; i++)
    {
        int k=nt[i];
        while(k>=0&&b[i]!=b[k])
            k=nt[k];
        nt[i+1]=k+1;
    }
}

int kmp()
{
    int i=0,j=0,sum=0;
    int kk=strlen(a);
    while(i<kk)
    {
        if(a[i]==b[j]||j==-1)
            i++,j++;
        else
            j=nt[j];
        if(j>=m) sum++,j=nt[j];
    }
    return sum;
}
int main()
{
    int n;
    while(~scanf("%d",&n))
    {
        scanf("%s%s",b,a);
        get_next();
        printf("%d\n",kmp());
    }
    return 0;
}