hdu 1686 Oulipo KMP匹配次数统计

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1686

分析：典型的KMP算法，统计字符串匹配的次数。 用Next数组压缩时间复杂度，要做一些修改。

/*Oulipo

Time Limit: 3000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 5769    Accepted Submission(s): 2322


Problem 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
*/
//KMP
#include <cstdio>
#include <cstring>
const int maxn = 10000 + 10, maxm = 1000000 + 10;
int next[maxn], len1, len2;
char a[maxn], b[maxm];
void getNext()
{
    int i, j = 0, k = -1;
    next[0] = -1;
    while(j < len1){
        if(k == -1 || a[j] == a[k]) next[++j] = ++k;
        else k = next[k];
    }
} 
int kmp()
{
    int i = 0, j = 0, ans = 0;
    while(i < len2){
        while(j != -1 && b[i] != a[j]) j = next[j];
        i++; j++;
        if(j >= len1){
            ans++;
            j = next[j];
        }
    }
    return ans;
}
int main()
{
    int T;
    scanf("%d", &T);
    while(T--){
        scanf("%s%s", a, b);
        len1 = strlen(a); len2 = strlen(b);
        getNext();
        printf("%d
", kmp());
    }
    return 0;
}