B - Oulipo

The French author Georges Perec (1936?C1982) 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. 

3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

1
3
0

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<vector>
#include<string>
#include<cstring>
using namespace std;
#define MAXN 1000001
typedef long long LL;
/*
KMP  查找子串出现的次数    
*/
char s[MAXN],t[MAXN];
int Next[MAXN];
void pre_kmp(int m)
{
    int j,k;
    j = 0;k = -1;Next[0] = -1;
    while(j<m)
        if(k==-1||t[k]==t[j])
            Next[++j] = ++k;
        else
            k = Next[k];
}
int KMP(char s[],char t[],int n,int m)
{
    int i,j,ans;
    i = j = ans = 0;
    if(n==1&&m==1)
        return (s[0]==t[0])?1:0;
    pre_kmp(m);
    for(i=0;i<n;i++)
    {
        while(j>0&&s[i]!=t[j])
            j = Next[j];
        if(s[i]==t[j])
            j++;
        if(j==m)
        {
            ans++;
            j = Next[j];
        }
    }
    return ans;
}
int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%s%s",t,s);
        printf("%d\n",KMP(s,t,strlen(s),strlen(t)));
    }
}