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.

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.

 1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 using namespace std; 5 char a[10001]; 6 char b[1000001]; 7 int  p[10001]; 8 int la,lb; 9 int j;10 int ans;11 inline void makep()12 {13     14     j=0;15     for(int i=1;i<la;i++)16     {17         while(j>0&&a[i]!=a[j])18         j=p[j];19         if(a[i]==a[j])20         j++;21         p[i]=j;22     }23     return ;24 }25 inline void KMP()26 {27     j=0;28     ans=0;29     for(int i=0;i<lb;i++)30     {31         while(b[i]!=a[j]&&j>0)32         j=p[j-1];33         if(b[i]==a[j])34         j++;35         if(j==la)36         {37             ans++;38             j=p[j-1];        39         }40         41     }42     printf("%d\n",ans);43     return ;44 }45 46 int main()47 {48     int n;49     scanf("%d",&n);50     51     for(int i=1;i<=n;i++)52     {53         memset(p,0,sizeof(p));54         scanf("%s%s",a,b);55         la=strlen(a);lb=strlen(b);56         makep();57         KMP();58     }59         60     61     return 0;62 }

TLE

AC

 1 #include<cstdio> 2 #include<cstdlib> 3 #include<cstring> 4 #include<iostream> 5 using namespace std; 6  7 int n,la,lb; 8 int next[100010]; 9 char a[1000010],b[100010];10 11 void getnext()12 {13     int j=-1;14     next[0]=-1;15     for(int i=1;i<lb;i++)16     {17         if(j!=-1 && b[j+1]!=b[i])    j=next[j];18         if(b[j+1]==b[i])    j++;19         next[i]=j;20     }21 }22 23 int kmp()24 {25     int ans=0;26     int j=-1;27     for(int i=0;i<la;i++)28     {29         if(j!=-1 && a[i]!=b[j+1])    j=next[j];30         if(b[j+1]==a[i])    j++;31         if(j==lb-1)    32         {33             ans++;    34             j=next[j];35         }    36     }37     return ans;38 }39 40 int main()41 {42     scanf("%d",&n);43     for(int u=1;u<=n;u++)44     {45         scanf("%s %s",b,a);46         la=strlen(a);47         lb=strlen(b);48         getnext();49         printf("%d\n",kmp());50     }51 }

AC