POJ 3461 Oulipo 【KMP统计子串数】

传送门：http://poj.org/problem?id=3461

Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 50450		Accepted: 20018

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

KMP模板：

#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
#define INF 0x3f3f3f3f
#define LL long long
using namespace std;
const int MAXN = 1e6+10;
const int MAXW = 1e4+10;
char W[MAXW], T[MAXN];
int wlen, tlen;
int nxt[MAXW];

void get_Next()
{
    int j = 0, k = -1;
    nxt[0] = -1;
    while(j < wlen){
        if(k == -1 || W[j] == W[k]){
            nxt[++j] = ++k;
        }
        else k = nxt[k];
    }
}

int KMP_count()
{
    int ans = 0, j = 0;
    if(wlen == 1 && tlen == 1){
        if(W[0] == T[0]) return 1;
        else return 0;
    }
    get_Next();
    for(int now = 0; now < tlen; now++){
        while(j > 0 && T[now] != W[j])
            j = nxt[j];
        if(W[j] == T[now]) j++;
        if(j == wlen){
            ans++;
            j = nxt[j];
        }
    }
    return ans;
}

int main()
{
    int T_case;
    scanf("%d", &T_case);
    while(T_case--){
        scanf("%s%s", &W, &T);
        wlen = strlen(W);
        tlen = strlen(T);

        printf("%d
", KMP_count());
    }
    return 0;
}