[POJ3461] Oulipo

目录

• Description
• Input
• Output
• Sample Input
• Sample Output
• Source
• 题解
  • $KMP$
  • 字符串$Hash$

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

题解

(KMP)

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;

const int Lp=10101,Ls=1001001;
int lp,ls,nt[Lp];
char p[Lp],s[Ls];

void Make_nt()
{
	int i=0,j=-1;
	nt[i]=-1;
	while(i<lp)
	{
		if(j==-1||p[i]==p[j])
			++i,++j,nt[i]=j;
		else j=nt[j];
	}
}

void KMP(int id)
{
	int i=id,j=0,Ans=0;
	while(i<ls&&j<lp)
	{
		if(j==-1||s[i]==p[j]) ++i,++j;
		else j=nt[j];
		if(j==lp) ++Ans,j=nt[j-1],--i;
	}
	printf("%d
",Ans);
}

int main()
{
	int T;
	for(scanf("%d",&T);T;--T)
	{
		scanf("%s%s",p,s);
		lp=strlen(p),ls=strlen(s);
		Make_nt(),KMP(0);
	}
	return 0;
}

---

字符串(Hash)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<cmath>
#include<cstdlib>
using namespace std;

typedef unsigned long long ull;
const int E=1000007;
const int L1=2000000,L2=10005;
int l1,l2;
char s1[L1],s2[L2];
ull power[L2],h1[L1],h2;

int main()
{
	int T,Ans;
	power[0]=1;
	for(int i=1;i<L2;++i) power[i]=power[i-1]*E;
	for(scanf("%d
",&T);T;--T)
	{
		scanf("%s
%s
",s2+1,s1+1);
		l1=strlen(s1+1),l2=strlen(s2+1);
		for(int i=1;i<=l1;++i) h1[i]=h1[i-1]*E+s1[i];
		h2=0;
		for(int i=1;i<=l2;++i) h2=h2*E+s2[i];
		Ans=0;
		for(int i=0;i<=l1-l2;++i)
			if(h2==(h1[i+l2]-h1[i]*power[l2]))
				++Ans;
		printf("%d
",Ans);
	}
	return 0;
}