kuangbin kmp B题

B - Oulipo

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

题解：

阅读题。KMP入门题。

代码：

#include <iostream>#include <cstdio>#include <algorithm>#include <cstring>using namespace std;const int maxn = 1000000+100;const int maxm = 10000+100;int nt[maxn];char s[maxn],t[maxm];int slen,tlen;void getNext(){    int j,k;    j=0;k=-1;nt[0]=-1;    while(j<tlen)    {        if(k==-1||t[j]==t[k])        {            nt[++j]=++k;        }        else        {            k=nt[k];        }    }}int KMP_count(){    int ans=0;    int i,j=0;    if(slen==1&&tlen==1)    {        if(s[0]==t[0])        {            return 1;        }        else            return 0;    }    getNext();    for(i=0;i<slen;i++)    {        while(j>0&&s[i]!=t[j])            j=nt[j];        if(s[i]==t[j])            j++;        if(j==tlen)        {            ans++;            j=nt[j];        }    }    return ans;}int main(){    int T;    cin>>T;    while(T--)    {       scanf("%s",t);       scanf("%s",s);       slen = strlen(s);       tlen = strlen(t);       cout<<KMP_count()<<endl;    }    return 0;}