C++之路进阶——poj3461（Oulipo）

Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 35694		Accepted: 14424

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

题解：

    kmp经典例题，因为题目说可压缩，所以末尾+1的失败指针指向1，1的失败指针指向0，就ok了。

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define maxn 1000000

using namespace std;

int next[maxn],n;
char W[maxn],T[maxn];

void getnext()
    {
        int j=0,k=-1;next[0]=-1;
        while (!j||W[j]!=0)
           {
                if (k==-1||W[j]==W[k])
                  {
                    j++,k++;
                    if (W[j]!=W[k]) next[j]=k;else next[j]=next[k];
               }else k=next[k];
           }
    }
    
int kmp()
    {
        int i=0,j=0,num=0;
        memset(next,0,sizeof(next));
        int T_len=strlen(T),W_len=strlen(W);
        getnext();
        while (i<T_len)
           {
                if (j==-1||T[i]==W[j]) i++,j++;
                   else j=next[j];
                if (j==W_len)
                  {
                        num++;
                        j=next[j];
                  }
           }
        return num;       
    }    

int main()
  {
      scanf("%d",&n);
      for (int i=1;i<=n;i++)
         {
              scanf("%s%s",W,T);
              printf("%d\n",kmp());
         }
      return 0;
  }