【POJ 3461】 Oulipo(KMP)
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Oulipo
Time Limit: 1000MS Memory Limit: 65536K
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:输入T组数据。每组数据两个字符串,你将第一个字符串在第二个字符串中出现的次数输出。如AZA在AZAZA中有2次,在AZAZAZA中有三次。
分析:典型的KMP问题。单模式匹配。
不懂KMP算法的请参考:
http://www.ruanyifeng.com/blog/2013/05/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm.html
#include "iostream"#include "cstdio"#include "cstring"#include "algorithm"using namespace std;const int maxn = 1e4+5;int next[maxn];char str1[maxn];char str2[1000005];/*/////简单但是会超时 void MakeNext( char *p ){ int i,k;//Q记录字符串下标 k是最大前后相同缀长度 int m = strlen(p);//字符串长度 next[0] = -1;//第一个字符串的前后缀长度为0 for( i=1 , k=0 ; i<m ; i++ ){ while( k>0 && p[i] != p[k] ){//求出p[0]-->p[i]的最大前后缀长度 k = next[k-1]; } if( p[i] == p[k] ){ k++; } next[i] = k; } } */void MakeNext( char *str ){ int n = strlen(str); int i = 0, j = -1; next[0] = -1; while( i < n ){ if( j == -1 || str[i] == str[j] ) next[++i] = ++j; else j = next[j]; }}int kmp( char *p,char *str ){ int n = strlen(p); int m = strlen(str); int i = 0; int j = 0; int cnt = 0; while( i<m && j<n ){ if( str[i] == p[j] || j == -1 ){ i++; j++; } else{ j = next[j]; } if( j == n ){ cnt++; j = next[j]; } } return cnt;}int main(){ int T; scanf("%d",&T); while(T--){ scanf("%s",str1); scanf("%s",str2); MakeNext( str1 ); int ans = kmp( str1,str2 ); printf("%d\n",ans); } return 0;}
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