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    详细KMP见http://blog.csdn.net/u014665013/article/details/37995355

    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 wordW and a textT, count the number of occurrences of W inT. All the consecutive characters of W must exactly match consecutive characters ofT. 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 stringW).
    • 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 wordW in the textT.

    Sample Input

    3
    BAPC
    BAPC
    AZA
    AZAZAZA
    VERDI
    AVERDXIVYERDIAN

    Sample Output

    1
    3
    0

    题意:

    找出在目标串中有多少模式串(相邻两串中可以重叠)

    代码

    #include <stdio.h>
    #include <string.h>
    int next[10005];
    char str1[1000005],str2[10005];
    void getnext(int len)//此处也可以将int next[]改写成  int* next[]
    {
    	int j,k;
    	j=0; k=-1; next[0]=-1;
    	while(j<len){
    		if(k==-1 ||str2[j]==str2[k]){
    			j++;
    			k++;
    			next[j]=k;
    		}
    		else k=next[k];
    	}
    }
    int kmp(int len1,int len2)//kmp算法
    {
    	int count=0;
        int i=0,j=0;
        getnext(len2);
        while(i<len1)
        {
            if(j==-1||str1[i]==str2[j]){
              ++i;
              ++j;   //j控制子串回溯和遍历 
            }
            else
             j=next[j];
            if(j == len2){
                count++;
                j = next[j];   //当有一个匹配成功的时候,相当于匹配失败,重新定位子串的匹配位置 
            }
        }
      return  count; 
    }
    int main()
    {
        int Case;
        int len1,len2;
        scanf("%d",&Case);
        getchar();//注意吸收空格 
        while(Case--)
        {
            gets(str2);
            gets(str1);
            len1 = strlen(str1), len2 = strlen(str2);
            printf("%d
    ",kmp(len1,len2));
        }
        return 0;
    }
    
    



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  • 原文地址:https://www.cnblogs.com/zswbky/p/5432131.html
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