HUD 1686 Oulipo（KMP）

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

 

Source

华东区大学生程序设计邀请赛_热身赛

#include<bits/stdc++.h>
using namespace std;
#define ll long long

const ll inf = 2000000000000;
const int mod = 1000000007;
const int maxn = 1000000 + 8;

int k, t, ne[maxn], num;

string a, b;

void getnext()
{
    ne[0] = ne[1] = 0;
    int len = a.size();
    for(int i = 1; i < len; i++)
    {
        int j = ne[i];
        while(j && a[i] != a[j])///寻找与这个字母相同的字母，若找不到，就一直往前跳
            j = ne[j];
        ne[i + 1] = a[i] == a[j] ? j + 1 : 0;///如果两个字母相同，则i和j都加加；否则j = 0，重新比较
    }
}

void kmp()
{
    int j = 0, len1 = a.size(), len2 = b.size();
    for(int i = 0; i < len2; i++)
    {
        while(j && a[j] != b[i])///寻找两个字母都相同的字母，如果找不到相同的，就一直往前跳
            j = ne[j];
        if(a[j] == b[i])///如果找到相同的，就让字符的对应下标++
           j++;
        if(j == len1)///如果字符此时的下标已经等于a的长度，就记一下数
            num++;
    }
}

int main()
{
    std::ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> t;
    while(t--)
    {
        num = 0;
        memset(ne, 0, sizeof(ne));
        cin >> a;
        cin >> b;
        getnext();
        kmp();
        cout << num << '\n';
    }
    return 0;
}