pku1200 Crazy Search

http://poj.org/problem?id=1200

hash入门，用karp-rabin做的

#include <stdio.h>
#include <string.h>
#define N 16000100

char s[1000100] = "\0", mark[26] = "\0";
char hash2[N] = "\0";
int hash1[26] = {0};
int n, nc;

int main()
{
    int i, j, sum = 0, ncn = 1, result = 0;
    scanf("%d%d%*c%s", &n, &nc, s);
    for(j=1,i=0; s[i]; i++)
    {
        if(!mark[s[i]-'a'])
        {
            mark[s[i]-'a'] = 1;
            hash1[s[i]-'a'] = j;
            j = j + 1;
            if(j == nc+1)
            {
                break;
            }
        }
    }
    sum += hash1[s[n-1]-'a'];
    for(i=n-1; i>=1; i--)
    {
        ncn = ncn * nc;
        sum += hash1[s[i-1]-'a']*ncn;
    }
    hash2[sum] = 1;
    result ++;
    for(i=n; s[i]; i++)
    {
        sum -= hash1[s[i-n]-'a']*ncn;
        sum *= nc;
        sum += hash1[s[i]-'a'];
        if(!hash2[sum])
        {
            hash2[sum] = 1;
            result ++;
        }
    }
    printf("%d\n", result);
    return 0;
}