kmp-poj3461 oulipu

Posted 2021-12-30 wengsy150943

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

作为一道kmp的例题放在这里。

int nt[1000005];
string w,t;//w是模式串，t是匹配串
void init()
    memset(nt,0,sizeof(nt));
    int l=t.length(),j(-1),i=0;
    nt[0]=-1;
    while(i!=l)
        if(j==-1||t[i]==t[j])
            nt[++i]=++j;
        else j=nt[j];
    

int kmp()
    int lw(w.length()),lt(t.length()),i=0,j=0,cnt(0);
    while(i!=lt&&j!=lw)
        if(t[i]==w[j]||j==-1)
            ++i,++j;
        else j=nt[j];
        if(j==lw)
            cnt++;
            j=nt[j];
        
    
    return cnt;