POJ 3461 Oulipo（KMP匹配）

最新推荐文章于 2020-07-22 02:59:48 发布

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本文介绍了一个基于文本匹配的比赛任务，旨在快速准确地计算给定单词在长文本中出现的次数，包括重叠情况。文章提供了一段C++代码实现，用于演示如何通过KMP算法高效解决这一问题。

Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 42854		Accepted: 17221

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

#include<iostream>
#include<algorithm>
#include<cstring>
#include<stdio.h>
using namespace std;
const int maxn =1e6+10;
char a[maxn],b[maxn];
void kmp_pre(char x[],int m,int next[])
{
    int i,j;
    j=next[0]=-1;
    i=0;
    while(i<m){
        while(-1!=j&&x[i]!=x[j])j=next[j];
        next[++i]=++j;
    }
}

int f[maxn];
int KMP_Count(char x[],int m,char y[],int n)
{
    int i,j;
    int ans=0;
    kmp_pre(x,m,f);
    i=j=0;
    while(i<n){
        while(-1!=j&&y[i]!=x[j])j=f[j];
        i++;j++;
        if(j>=m){
            ans++; j=f[j];
        }
    }
    return ans;
}
int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%s%s",a,b);
        int l1=strlen(a);
        int l2=strlen(b);
        printf("%d\n",KMP_Count(a,l1,b,l2));
    }
}