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 题意:给你一个匹配串,一个文本串,求匹配串在文本串出现的次数 思路:KMP的基本应用#include <iostream> #include <cstdio> #include <cstring> #include <algorithm> using namespace std; const int maxn = 1000010; char a[maxn], b[maxn]; int next[maxn]; int n, m; void getnext() { int m = strlen(a); next[0] = 0, next[1] = 0; for (int i = 1; i < m; i++) { int j = next[i]; while (j && a[i] != a[j]) j = next[j]; next[i+1] = a[i] == a[j] ? j+1 : 0; } } int kmp() { int ans = 0; int n = strlen(b); int m = strlen(a); int j = 0; for (int i = 0; i < n; i++) { while (j && a[j] != b[i]) j = next[j]; if (a[j] == b[i]) j++; if (j == m) ans++; } return ans; } int main() { int t; scanf("%d", &t); while (t--) { scanf("%s%s", a, b); getnext(); int ans = kmp(); printf("%d\n", ans); } return 0; }