hdu 1686 Oulipo（kmp）

 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

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

#define M 1000010
int ne[M];
char a[M], b[10010];

void GetNext()
{
    int len = strlen(b);
    int i = 0, j = -1;
    while(i < len)
    {
        if(j == -1 || b[i] == b[j]){
            ne[++i] = ++j;
        }
        else j = ne[j];     //回溯至上一个
    }
}

int KmpCompare()
{
    int lena = strlen(a);
    int lenb = strlen(b);
    int i = 0, j = 0, s = 0;
    while(i<lena)
    {
        if(j == -1 || a[i] == b[j]){
            j++;
            i++;
            //cout <<i << ' ' << j<<endl;
        }
        else j = ne[j];
        if(j == lenb){
            j = ne[j];
            s++;
        }
    }
    return s;
}

int main()
{
    int t, s;
    scanf("%d", &t);
    while(t--){
        memset(ne, -1, sizeof(ne));
        scanf("%s", &b);
        //cout<<b;
        //getchar();
        scanf("%s", &a);
        //cout<<a;
        GetNext();
        s = KmpCompare();
        printf("%d\n", s);
    }
    return 0;
}

tle了无数遍。。。气死了。。。一定要用scanf，即使要用 cin 也别忘了取消cin与stdin的同步