[kuangbin带你飞]专题十六 KMP & 扩展KMP & Manacher B

B - Oulipo HDU - 1686

题目链接：https://vjudge.net/contest/70325#problem/B

题目：

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.

InputThe 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.
OutputFor 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
题意：给你两个字符串a,b,求出a在b中出现了多少次，用kmp即可

//
// Created by hanyu on 2019/8/13.
//
#include <algorithm>
#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <set>
#include<math.h>
#include<map>
using namespace std;
typedef long long ll;
const int maxn=1e6+10;
char str[maxn],str1[maxn];
int nextt[maxn];
void getnext()
{
    memset(nextt,0,sizeof(nextt));
    int i=0,j=-1;
    nextt[0]=-1;
    int m=strlen(str1);
    while(i<m)
    {
        if(j==-1||str1[i]==str1[j])
        {
           ++i,++j;
            if(str1[i]!=str1[j])
                nextt[i]=j;
            else
                nextt[i]=nextt[j];
        } else
            j=nextt[j];
    }
}
int kmp()
{
    int res=0;
    int n=strlen(str);
    int m=strlen(str1);
    int i=0,j=0;
    while(i<n){
        if(j==-1||str[i]==str1[j])
            i++,j++;
        else
            j=nextt[j];
        if(j==m)
        {
            j=nextt[j];
            res++;
        }
    }
    return res;
}
int main()
{
    int T;
    scanf("%d",&T);
    getchar();
    while(T--)
    {
        gets(str1);
        gets(str);
        getnext();
        printf("%d
",kmp());
    }
    return 0;
}