HDU 1381 Crazy Search

Crazy Search

Time Limit: 5000ms

Memory Limit: 32768KB

This problem will be judged on HDU. Original ID: 1381
64-bit integer IO format: %I64d      Java class name: Main

Many people like to solve hard puzzles some of which may lead them to madness. One such puzzle could be finding a hidden prime number in a given text. Such number could be the number of different substrings of a given size that exist in the text. As you soon will discover, you really need the help of a computer and a good algorithm to solve such a puzzle.

Your task is to write a program that given the size, N, of the substring, the number of different characters that may occur in the text, NC, and the text itself, determines the number of different substrings of size N that appear in the text.

As an example, consider N=3, NC=4 and the text "daababac". The different substrings of size 3 that can be found in this text are: "daa", "aab", "aba", "bab", "bac". Therefore, the answer should be 5. 

 

Input

The first line of input consists of two numbers, N and NC, separated by exactly one space. This is followed by the text where the search takes place. You may assume that the maximum number of substrings formed by the possible set of characters does not exceed 16 Millions.

 

Output

The program should output just an integer corresponding to the number of different substrings of size N found in the given text.
The first line of a multiple input is an integer N, then a blank line followed by N input blocks. Each input block is in the format indicated in the problem description. There is a blank line between input blocks.

The output format consists of N output blocks. There is a blank line between output blocks.

 

Sample Input

1

3 4
daababac

Sample Output

5

解题：很犀利的hash大法

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 const int maxn = 16000010;
 6 int bs[256],cnt,n,base,ans,T;
 7 char str[1000010];
 8 bool hs[maxn];
 9 int main() {
10     scanf("%d",&T);
11     while(T--) {
12         scanf("%d%d%s",&n,&base,str);
13         int len = strlen(str);
14         memset(hs,false,sizeof(hs));
15         for(int i = cnt = 0; i < len; ++i)
16             if(!bs[str[i]]) {
17                 bs[str[i]] = cnt++;
18                 if(cnt == base) break;
19             }
20         for(int i = ans = 0; i + n <= len; ++i) {
21             unsigned int hashV = 0;
22             for(int j = 0; j < n; j++)
23                 hashV = hashV*base + bs[str[i+j]];
24             if(!hs[hashV]) {
25                 hs[hashV] = true;
26                 ans++;
27             }
28         }
29         printf("%d\n",ans);
30         if(T) puts("");
31     }
32     return 0;
33 }

View Code

 

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