POJ 3461 Oulipo （KMP算法）

最新推荐文章于 2019-08-17 11:00:30 发布

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最新推荐文章于 2019-08-17 11:00:30 发布

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原文链接：http://www.cnblogs.com/toyking/p/3797405.html

本文详细介绍了一道经典的字符串匹配问题，并使用KMP算法解决该问题。文章通过一个具体的编程比赛题目来阐述如何快速查找一个字符串在另一长字符串中的所有出现位置。

Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 21682		Accepted: 8648

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组测试数据，每组两行分别为word和text，问你text中包含多少个word子串。

解题思路：

较裸的一题KMP算法，关于KMP算法，参照：http://www.cppblog.com/oosky/archive/2006/07/06/9486.html

解题代码：

#include <iostream>
#include <cstdio>
#include <vector>
#include <cstring>
#include <string>
using namespace std;

const int maxn=11000;
int next[maxn];

char word[maxn],text[maxn*100];

void kmp(){
    int n=strlen(word);
    for(int i=0;i<=n;i++) next[i]=0;
    for(int i=1;i<n;i++){
        int j=i;
        while(j>0){
            j=next[j];
            if(word[j]==word[i]){
                next[i+1]=j+1;
                break;
            }
        }
    }
    int m=strlen(text),ret=0;
    for(int i=0,j=0;i<m;i++){
        if( j<n && text[i]==word[j]){
            j++;
        }else{
            while(j>0){
                j=next[j];
                if(text[i]==word[j]){
                    j++;
                    break;
                }
            }
        }
        if(j==n){
            ret++;
        }
    }
    printf("%d\n",ret);
}

int main(){
    int t;
    scanf("%d\n",&t);
    while(t-- >0){
        scanf("%s%s",word,text);
        kmp();
    }
    return 0;
}

转载于:https://www.cnblogs.com/toyking/p/3797405.html