POJ 3461 kmp

Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 40168		Accepted: 16135

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

 

莫名其妙TLE

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
char a[10001];
char b[1000001];
int  p[10001];
int la,lb;
int j;
int ans;
inline void makep()
{
    
    j=0;
    for(int i=1;i<la;i++)
    {
        while(j>0&&a[i]!=a[j])
        j=p[j];
        if(a[i]==a[j])
        j++;
        p[i]=j;
    }
    return ;
}
inline void KMP()
{
    j=0;
    ans=0;
    for(int i=0;i<lb;i++)
    {
        while(b[i]!=a[j]&&j>0)
        j=p[j-1];
        if(b[i]==a[j])
        j++;
        if(j==la)
        {
            ans++;
            j=p[j-1];        
        }
        
    }
    printf("%d\n",ans);
    return ;
}

int main()
{
    int n;
    scanf("%d",&n);
    
    for(int i=1;i<=n;i++)
    {
        memset(p,0,sizeof(p));
        scanf("%s%s",a,b);
        la=strlen(a);lb=strlen(b);
        makep();
        KMP();
    }
        
    
    return 0;
}

 

AC

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
using namespace std;

int n,la,lb;
int next[100010];
char a[1000010],b[100010];

void getnext()
{
    int j=-1;
    next[0]=-1;
    for(int i=1;i<lb;i++)
    {
        if(j!=-1 && b[j+1]!=b[i])    j=next[j];
        if(b[j+1]==b[i])    j++;
        next[i]=j;
    }
}

int kmp()
{
    int ans=0;
    int j=-1;
    for(int i=0;i<la;i++)
    {
        if(j!=-1 && a[i]!=b[j+1])    j=next[j];
        if(b[j+1]==a[i])    j++;
        if(j==lb-1)    
        {
            ans++;    
            j=next[j];
        }    
    }
    return ans;
}

int main()
{
    scanf("%d",&n);
    for(int u=1;u<=n;u++)
    {
        scanf("%s %s",b,a);
        la=strlen(a);
        lb=strlen(b);
        getnext();
        printf("%d\n",kmp());
    }
}