HASH处理KMP算法

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring> 
 4 using namespace std;
 5 const int Bas = 131, M = 1e6 + 10;
 6 char a[M],b[M];
 7 long long la,lb;
 8 long long sumv[M],mil[M],key;
 9 long long get(long long l,long long r)
10 {
11     return sumv[r]-sumv[l]*mil[la];
12 }
13 int main()
14 {
15     key=0;
16     memset(sumv,0,sizeof sumv);
17     scanf("%s%s",b+1,a+1);
18     la=strlen(a+1),lb=strlen(b+1),mil[0]=1;
19     for (int i=1;i<=la;++i) key=key*Bas+(int)a[i];
20     for (int i=1;i<=lb;++i) 
21         sumv[i]=sumv[i-1]*Bas+(int)b[i],mil[i]=mil[i-1]*Bas;
22     int ans=0;
23     for (int i=0;i<=lb-la;++i)
24         if (key==get(i,i+la)) ++ans;
25     cout<<ans<<endl;
26     return 0;
27 }