HDU 1686

传送门：http://acm.hdu.edu.cn/showproblem.php?pid=1686

Oulipo

Time Limit: 3000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 9226 Accepted Submission(s): 3718

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

简单的KMP。

#include"iostream"#include"cstdio"#include"cstring"using namespace std;int nexts[100005];char s1[10000005],s2[100005];bool flag;void get_nexts(string s2,int nexts[]){    int i=0,k=-1;    nexts[0]=-1;    while(i<s2.length())    {        if(k == -1 || s2[i]==s2[k])        {            i++;            k++;            if(s2[i] == s2[k])                nexts[i] =nexts[k];            else nexts[i] =k;        }        else            k=nexts[k];    }}int kmp(string s1,string s2,int nexts[]){    int i=0,j=0,ans=0;    while(i<s1.length())    {        if(j== -1||s1[i]==s2[j])        {            i++;            j++;        }        else            j=nexts[j];        if(j==s2.length())        {            ans++;            j=nexts[j];     //这里需要注意的是 J 匹配成功后返回nexts[j]可以更节省时间。而不是J=0;        }    }    /*if(s2[j]=='\0')        ans++;*/    return ans;}int main(){    int t;    scanf("%d",&t);    getchar();    while(t--)    {        scanf("%s%s",s2,s1);        get_nexts(s2,nexts);        int ans=kmp(s1,s2,nexts);        printf("%d\n",ans);    }    return 0;}