【kmp】POJ-3461 Oulipo

附上题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=10368

Oulipo

Time Limit: 1000MS Memory Limit: 65536KB 64bit IO Format: %I64d & %I64u

Submit Status

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

Source

BAPC 2006 Qualification

不多说，一道裸的kmp。。。只不过是求个数而不是求位置，于是乎刚开始时被光荣的坑了。。。找到一个后不是j=0；而是j = next[j]，因为要充分利用好next这个资源，next是最大前缀后缀相同的长度。。。。也就是说w串只需移动j - next[j]个长度就够了，因为前面是相同的，不需重新比较。。

【代码】：

#include<cstdio>#include<iostream>#include<cstring>using namespace std;char w[10000 + 5];char t[1000000 + 5];int next[10000 + 5];int T;int ans = 0;void getnext(int &w_len){int k = -1,j = 0;next[0] = -1;while(j < w_len){if(k == -1 || w[k] == w[j]){j++;k++;if(w[j] != w[k]) next[j] = k;else next[j] = next[k];}else k = next[k];}}void kmp(int &w_len,int &t_len){int i = 0, j = 0;while(i < t_len && j < w_len){if(t[i] == w[j] || j == -1){i++;j++;}else j = next[j];if(j == w_len){ans++;j = next[j];}}}int main(){scanf("%d", &T);while(T--){ans = 0;scanf("%s",w);scanf("%s",t);int w_len = strlen(w);int t_len = strlen(t);getnext(w_len);kmp(w_len, t_len);printf("%d\n",ans);}return 0;}