[POJ] 3461 Oulipo [KMP算法]

Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 23667		Accepted: 9492

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

Sample Output

1
3
0

Source

BAPC 2006 Qualification

 

 

题解: 统计W串在T串中出现的次数。根据数据规模，KMP算法可AC。

 

代码：

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<ctype.h>
#include<stdlib.h>
#include<stdbool.h>

#define rep(i,a,b)      for(i=(a);i<=(b);i++)
#define clr(x,y)        memset(x,y,sizeof(x))
#define sqr(x)          (x*x)
#define LL              long long

int i,j,n,num,
    f[1000003];

char p[10003],t[1000003];

int init()
{
    clr(p,'');
    clr(t,'');
    clr(f,0);
    num=0;
    
    scanf("%s",p);
    scanf("%s",t);
    
    return 0;
}

void kmp(char *t, char *p, int *f)
{
    int n,m,j;
    n = strlen(t); m = strlen(p);
    getFail(p,f);
    
    j = 0;
    
    for(i = 0;i < n;i++) {
        while(j && p[j] != t[i]) j=f[j];
        if(p[j] == t[i]) j++;
        if(j == m) num++;
    }

    
}

void getFail(char p[],int f[])
{
    int m,j,i;
    m = strlen(p);
    f[0] = 0;f[1] = 0;

    for(i = 1;i < m;i++) {
        j = f[i];
        while(j && p[i] != p[j]) j = f[j];
        f[i+1]=p[i]==p[j] ? j+1 : 0;
    }
}

int main()
{
    int T;
    scanf("%d",&T);
    
    while(T--) {
        init();
        getFail(p,f);
        kmp(t,p,f);
        printf("%d
",num);
    }
    return 0;
}