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    The French author Georges Perec (1936�C1982) 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. 

    InputThe 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. 
    OutputFor 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
    #include<iostream>
    #include<algorithm>
    #include<cstdio>
    #include<vector>
    #include<string>
    #include<cstring>
    using namespace std;
    #define MAXN 1000001
    typedef long long LL;
    /*
    KMP  查找子串出现的次数    
    */
    char s[MAXN],t[MAXN];
    int Next[MAXN];
    void pre_kmp(int m)
    {
        int j,k;
        j = 0;k = -1;Next[0] = -1;
        while(j<m)
            if(k==-1||t[k]==t[j])
                Next[++j] = ++k;
            else
                k = Next[k];
    }
    int KMP(char s[],char t[],int n,int m)
    {
        int i,j,ans;
        i = j = ans = 0;
        if(n==1&&m==1)
            return (s[0]==t[0])?1:0;
        pre_kmp(m);
        for(i=0;i<n;i++)
        {
            while(j>0&&s[i]!=t[j])
                j = Next[j];
            if(s[i]==t[j])
                j++;
            if(j==m)
            {
                ans++;
                j = Next[j];
            }
        }
        return ans;
    }
    int main()
    {
        int T;
        scanf("%d",&T);
        while(T--)
        {
            scanf("%s%s",t,s);
            printf("%d
    ",KMP(s,t,strlen(s),strlen(t)));
        }
    }
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  • 原文地址:https://www.cnblogs.com/joeylee97/p/6671069.html
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