C++-POJ1200-Crazy Search[hash]

由于已经给出字符只有NC种，故可以把子串视为一个NC进制的数，以此构造hash函数就可以了

 #include <set>
 #include <map>
 #include <cmath>
 #include <queue>
 #include <vector>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 using namespace std;
 const int MAXN=;
 char s[MAXN];int hash[MAXN],num[];
 int main(){
     for(int N,NC;scanf("%d%d",&N,&NC)!=EOF;){
         memset(hash,,sizeof(hash));
         memset(num,,sizeof(num));
         scanf("%s",s+);
         int cnt=,ans=,len=strlen(s+);
         for(int i=;i<=len&&cnt<=NC;i++)if(!num[s[i]])num[s[i]]=cnt++;
         for(int i=;i<=len-N+;i++){
             int hashi=;for(int j=i;j<=i+N-;j++)hashi=hashi*NC+num[s[j]];
             hash[hashi]?:ans++,hash[hashi]=;
         }
         cout<<ans<<endl;
     }
     return ;
 }