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=16000001;
char s[MAXN];int hash[MAXN],num[130];
int main(){
    for(int N,NC;scanf("%d%d",&N,&NC)!=EOF;){
        memset(hash,0,sizeof(hash));
        memset(num,0,sizeof(num));
        scanf("%s",s+1);
        int cnt=0,ans=0,len=strlen(s+1);
        for(int i=1;i<=len&&cnt<=NC;i++)if(!num[s[i]])num[s[i]]=cnt++;
        for(int i=1;i<=len-N+1;i++){
            int hashi=0;for(int j=i;j<=i+N-1;j++)hashi=hashi*NC+num[s[j]];
            hash[hashi]?0:ans++,hash[hashi]=1;
        }
        cout<<ans<<endl;
    }
    return 0;
}