KMP 字符串匹配 POJ 3461 Oulipo

Oulipo

Time limit            1000 ms

Memory limit        65536 kB

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 wordW and a text T, count the number of occurrences of W inT. All the consecutive characters of W must exactly match consecutive characters ofT. 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 stringW).
• 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 wordW in the text T.

Sample Input

3BAPCBAPCAZAAZAZAZAVERDIAVERDXIVYERDIAN

Sample Output

130

        一道比较典型的KMP，只是在处理子串的回溯时要注意利用next数组优化，不然会超时。

        另外，在输入输出时要使用scanf，如果用cin也会超时，之前是个讲过这个问题，第一次遇到，以后注意。

#include<cstdio>#include<iostream>#include<cstring>using namespace std;char a[1000005];char b[10005];int lena,lenb;int next[10005];void getnext(){    int i=0,k=-1;    next[0]=-1;     //next[0]=0    while(i<lenb)    {        if(k==-1||b[i]==b[k])        {            i++;            k++;            next[i]=k;      //注意：next[i]是子串前i个字符的最大公共长度，即b[i-1]（字符数组是从0开始存储的）        }        else            k=next[k];    }}int KMP(){    getnext();    int i=0,j=0;    int cnt=0;    while(i<lena)    {        if(j==-1||a[i]==b[j])        {            i++;            j++;        }        else            j=next[j];        if(j==lenb)        {            cnt++;            j=next[lenb];        }    }    return cnt;}int main(){    int n;    while(scanf("%d",&n)!=EOF)    {        memset (a, 0, sizeof (a));        memset (b, 0, sizeof (b));        for (int i=0; i<n; i++)        {            scanf("%s",b);            scanf("%s",a);            lena=strlen(a);            lenb=strlen(b);            printf("%d\n",KMP());        }    }    return 0;}