hash poj_1200 Crazy Search

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
using namespace std;
int n,nc;
char s[1000000];
int _hash[16000005],num[257];
int main()
{
//    freopen("in","r",stdin);
    while(scanf("%d%d",&n,&nc)!=EOF)
    {
        memset(_hash,0,sizeof(_hash));
        memset(num,0,sizeof(num));
        memset(s,'\0',sizeof(s));
        scanf("%s",s);
        int len=strlen(s);
        int seed=0;
//        printf("here\n");
        for(int i=0;i!=len;i++)
        {
            if(!num[s[i]])
            {
                num[s[i]]=++seed;
            }
            if(seed==nc)
            {
                break;
            }
        }
//        printf("here\n");
        int sum=0;
        int ans=0;
        for(int i=0;i<=len-n;i++)
        {
            sum=0;
            for(int j=0;j<n;j++)
            {
                sum=sum*nc+num[s[i+j]]-1;
            }
            if(!_hash[sum])
            {
                _hash[sum]=1;
                ans++;
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}

 简单 hash

这里有比较全的字符串hash

https://www.byvoid.com/blog/string-hash-compare/