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  • kmp

    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
     1 #include<stdio.h>
     2 #include<string.h>
     3 #define N 1000005
     4 char s[N];
     5 char p[N];
     6 int next[N];
     7 int m,n;
     8 void getnext()
     9 {
    10     int j=0,k=-1;
    11     next[0]=-1;
    12     while(j<m)
    13     {
    14         if(k==-1||p[j]==p[k])
    15         {
    16             j++;
    17             k++;
    18             next[j]=k;
    19         }
    20         else
    21             k=next[k];
    22     }
    23 }
    24 int kmp()
    25 {
    26     int i=0,j=0,ans=0;
    27     getnext();
    28     while(i<n)
    29     {
    30         if(j==-1||s[i]==p[j])
    31         {
    32             i++;
    33             j++;
    34         }
    35         else
    36             j=next[j];
    37         if(j==m)
    38             ans++;
    39     }
    40     return ans;
    41 }
    42 int main()
    43 {
    44     int t;
    45     scanf("%d",&t);
    46     while(t--)
    47     {
    48         scanf(" %s %s",&p,&s);
    49         m=strlen(p);
    50         n=strlen(s);
    51         printf("%d
    ",kmp());
    52     }
    53     return 0;
    54 }
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  • 原文地址:https://www.cnblogs.com/moomcake/p/8987022.html
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