Oulipo (KMP算法）

題目連結:HDU-1686

題目：

Oulipo

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

題目大意：在字元串T中找出字元串W出現的次數。

例：

W:AZA

T: AZAZAZA

T中包含AZAZAZA，AZAZAZA，AZAZAZA共3個，是以答案為3

AC代碼：

#include<iostream>
#include<cstring>
using namespace std;

char w[10005];
char t[1000005];
int nex[10005];

void getnext(int nex[],char w[],int l)//計算next數組，l為字元串w的長度
{
    int i=0,j = -1;
    nex[0] = -1;
    while(i<l)
    {
        if(j == -1||w[i]==w[j])
        {
            i++;
            j++;
            nex[i]=j;
        }
        else
            j=nex[j];
    }
}

int kmp(char t[],char w[],int l1,int l2)
{
    int ans=0;
    int i=0,j=0;
    while(i<l1)//周遊1遍字元串t
    {
        if(j==-1||t[i]==w[j])
        {
            i++;
            j++;
        }
        else
            j=nex[j]; 
        if(j==l2)
        {
            ans++;
            j=nex[j];//完成比對後進入下一次比對，直到周遊完字元串t
        }       
    }
    return ans;
}

int main()
{
    int q;
    cin >> q;
    while(q--)
    {
        cin >> w;
        cin >> t;
        getnext(nex,w,strlen(w));       
        cout << kmp(t,w,strlen(t),strlen(w)) << endl;
    }
    return 0;
}