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
这是一道考KMP的算法题,需要注意的是当匹配了一个模式串P后,如何选择i和j。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <iostream>
using namespace std;
char T[1000010], P[10010];
int f[10010];
void KMPFailureFunction()
{
int i, j;
int m = strlen(P);
i = 1;
j = 0;
while(i < m)
{
if(P[j] == P[i])
{
f[i] = j + 1;
++i;
++j;
} else if(j > 0)
j = f[j - 1];
else {
f[i] = 0;
++i;
}
}
}
int KMP()
{
KMPFailureFunction();
int ans = 0;
int i, j;
int n = strlen(T);
int m = strlen(P);
i = 0;
j = 0;
while(i < n)
{
if(P[j] == T[i])
{
if(j == m-1)
{
ans++;
++i; j = f[j];
} else {
++i;
++j;
}
} else if(j > 0)
j = f[j - 1];
else ++i;
}
return ans;
}
int main()
{
//freopen("data_B.txt", "r", stdin);
int t;
scanf("%d", &t);
while(t--)
{
scanf("%s%s", P, T);
printf("%d\n", KMP());
}
return 0;
}