pku1200 Crazy Search

http://poj.org/problem?id=1200
hash入门，用karp-rabin做的
 1 #include <stdio.h>
 2 #include <string.h>
 3 #define N 16000100
 4 
 5 char s[1000100] = "\0", mark[26] = "\0";
 6 char hash2[N] = "\0";
 7 int hash1[26] = {0};
 8 int n, nc;
 9 
10 int main()
11 {
12     int i, j, sum = 0, ncn = 1, result = 0;
13     scanf("%d%d%*c%s", &n, &nc, s);
14     for(j=1,i=0; s[i]; i++)
15     {
16         if(!mark[s[i]-'a'])
17         {
18             mark[s[i]-'a'] = 1;
19             hash1[s[i]-'a'] = j;
20             j = j + 1;
21             if(j == nc+1)
22             {
23                 break;
24             }
25         }
26     }
27     sum += hash1[s[n-1]-'a'];
28     for(i=n-1; i>=1; i--)
29     {
30         ncn = ncn * nc;
31         sum += hash1[s[i-1]-'a']*ncn;
32     }
33     hash2[sum] = 1;
34     result ++;
35     for(i=n; s[i]; i++)
36     {
37         sum -= hash1[s[i-n]-'a']*ncn;
38         sum *= nc;
39         sum += hash1[s[i]-'a'];
40         if(!hash2[sum])
41         {
42             hash2[sum] = 1;
43             result ++;
44         }
45     }
46     printf("%d\n", result);
47     return 0;
48 }