题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=1686
Time Limit: 3000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
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
题目大意:给出一个模式串和一个文本串,求文本串中模式串出现了几次。
解题思路:直接使用KMP算法。
1 #include<cstdio>
2 #include<cstring>
3 #include<iostream>
4 #define MAXpat 10000+5
5 #define MAXstr 1000000+5
6 using namespace std;
7 int Next[MAXpat];
8 char str[MAXstr],pat[MAXpat];
9
10 void getNext()
11 {
12 int i=0, j=-1, len=strlen(pat);
13 Next[0]=-1;
14 while(i<len)
15 {
16 if(j == -1 || pat[i] == pat[j]) Next[++i]=++j;
17 else j=Next[j];
18 }
19 }
20 int kmp()
21 {
22 int i=0, j=0, len1=strlen(str), len2=strlen(pat);
23 int ans=0;
24 while(i<len1)
25 {
26 if(j == -1 || str[i] == pat[j]) i++, j++;
27 else j=Next[j];
28 if(j == len2) ans++;
29 }
30 return ans;
31 }
32
33 int main()
34 {
35 int t;
36 scanf("%d",&t);
37 while(t--)
38 {
39 scanf("%s%s",pat,str);
40 getNext();
41 printf("%d\n",kmp());
42 }
43 }