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A - Oulipo
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
3BAPCBAPCAZAAZAZAZAVERDIAVERDXIVYERDIAN
Sample Output
130
在刚开始用ci.get()一个个的输入字符，然后竟然超时了，然后就直接将一行输入，就ac了，可见每次单独的IO操作都会耗费一定的时间，而且耗费的时间还不短。
#include<iostream>
using namespace std;
char text[1000005];
char w[10005];
int nex[10005];
void findNext(int n)
{
nex[0]=-1;
int i=0;
int k=-1;
while(i<n)
{
if(-1==k || w[nex[i]]==w[i])
{
i++;
k++;
nex[i]=k;
}
else
{
k=nex[k];
}
}
}
int kmp(int n,int m)
{
int i=0;
int j=0;
int num=0;
while(i<n)
{
if(text[i]==w[j])
{
i++; j++;
}
else
{
j=nex[j];
}
if(j==m)
{
j=nex[j];
num++;
}
if(-1==j)
{
j=0; i++;
}
}
return num;
}
int main()
{
int N;
cin>>N;
cin.get();
int n=0,m=0;
while(N--)
{
n=0;m=0;
cin>>w;
m=strlen(w);
cin>>text;
n=strlen(text);
findNext(m);
int num=kmp(n,m);
cout<<num<<endl;
}
}
A - Oulipo