【字符串入门专题1】J - Oulipo hdu1686 【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.
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.
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
题意：用字符串1做模式串，字符串2做匹配串，输出匹配串的总数，允许重叠匹配
思路：kmp模板的套用，我自己思维没转过弯，所以wrong了一次，看了一下别人的题解才知道，允许重叠匹配的话，当匹配到模式串的末尾时，不能直接让j从0重新开始，而是利用next数组，让j回到最大匹配坐标。
#include<cstring>
#include<cstdio>
#define N 1100000
#define M 11000
char s2[M],s1[N];
int NEXT[M];
void getNext(char s2[],int next[])
{
int i,j,k;
k = -1;
j = 0;
next[0] = -1;//划重点！！！已经n多次忘记初始化了！！
while(s2[j]!='\0')
{
while(k!=-1&&s2[j]!=s2[k])
k = next[k];
k++;
j++;
if(s2[k]!=s2[j])
next[j] = k;
else
next[j] = next[k];
}
return;
}
void kmp(char s1[],char s2[],int next[])
{
int i,j,count;
i = j = count = 0;
while(s1[i]!='\0')
{
while(j!=-1&&s1[i] != s2[j])
j = next[j];
j++;
i++;
if(s2[j]=='\0')
{
j = next[j];
count ++;
}
}
printf("%d\n",count);
return;
}
int main()
{
int t;
scanf("%d",&t);
while(t --)
{
scanf("%s",s2);
scanf("%s",s1);
getNext(s2,NEXT);
kmp(s1,s2,NEXT);
}
return 0;
}
