• hdu Oulipo(kmp)


    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
     
    Source
     
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    代码:

     1 #include <vector>
     2 #include <map>
     3 #include <set>
     4 #include <algorithm>
     5 #include <iostream>
     6 #include <cstdio>
     7 #include <cmath>
     8 #include <cstdlib>
     9 #include <string>
    10 #include <cstring>
    11 #include <queue>
    12 using namespace std;
    13 #define INF 0x3f3f3f3f
    14 
    15 char p[10010],s[1000010];
    16 int nex[10010];
    17 
    18 void get(char *p)
    19 {
    20     int plen=strlen(p);
    21     nex[0]=-1;
    22     int k=-1,j=0;
    23     while(j < plen){
    24         if(k==-1 || p[j] == p[k]){
    25             ++j;
    26             ++k;
    27             if(p[j] != p[k])
    28                 nex[j]=k;
    29             else
    30                 nex[j]=nex[k];
    31         }
    32         else{
    33             k=nex[k];
    34         }
    35     }
    36 }
    37 
    38 int kmp(char *s,char *p)
    39 {
    40     int i=0,j=0,ans=0;
    41     int slen=strlen(s);
    42     int plen=strlen(p);
    43     while(i < slen && j< plen){
    44         if(j==-1 || s[i]==p[j]){
    45             ++i;
    46             ++j;
    47         }
    48         else{
    49             j=nex[j];
    50         }
    51         if(j == plen){  //重点注意,这里是为了回到当匹配完后,next[j]应该回到的位置 
    52             j=nex[j];   //例: a="aza" b="azazaza" 第一次结束后,next[j]应该所指的位置为a中的‘z’,然后继续匹配  
    53             ans++;
    54         }
    55     }
    56 
    57     return ans;
    58 }
    59 
    60 int main()
    61 {
    62     int t;
    63     scanf("%d",&t);
    64     while(t--){
    65         scanf("%s",p);
    66         scanf("%s",s);
    67         get(p);
    68         printf("%d
    ",kmp(s,p));
    69     }
    70 }
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  • 原文地址:https://www.cnblogs.com/wangmengmeng/p/5487252.html
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