【poj3461】Oulipo

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.

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.

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.

题解

题目意思：求a串在b串出现的次数

直接kmp

#include<iostream>
#include<cstdio>
#include<cstring>
#define N 1000010
using namespace std;
int fail[N],f[N],kmp;
int main()
{
    freopen("oulipo.in","r",stdin);
    freopen("oulipo.out","w",stdout);
    int T;
    scanf("%d",&T);
    for (int I= 1;I<=T;I++)
    {
        int ans = 0;
        char s1[N],s2[N];
           scanf("%s%s",s2+1,s1+1);
        int l1=strlen(s1+1),l2=strlen(s2+1);
      //    cout<<l1<<endl<<l2<<endl;
        fail[1] = 0;
        for (int i=2;i<=l2;i++)
        {
            int p = fail[i-1];
            while (p && s2[p+1] !=s2[i]) p=fail[p];
            if (s2[p+1] == s2[i]) p++;
            fail[i] = p;
        }
        int p=0;
        for (int i=1;i<=l1;i++)
        {
            while (p && s2[p+1] != s1[i]) p=fail[p];
            if (s2[p+1] == s1[i]) p++;
            f[i] = p;
            if (p == l2)
            {
                ans++;
               // printf("%d",i-l2+1);
                //break;
            }
        }
    //    for (int i=1;i<=l2;i++) 
    //    printf("%d ",fail[i]);printf (" \n");
    //    for (int i=1;i<=l1;i++) printf("%d ",f[i]);
        printf("%d\n",ans);
    }
}