字符串Hash 斤斤计较的小Z

#include<bits/stdc++.h>
using namespace std;
const int N=1e6+5;
char p[N],s[N];//
typedef unsigned long long ull;//
const ull base=131;// 
ull h1[N],h2[N],b[N];

ull getHash(ull h[],int l,int r) //
{
  return h[r]-h[l-1]*b[r-l+1];
}

int main()
{
  ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    cin>>p+1;int m=strlen(p+1);//p+1表示匹配时从下标1开始
    cin>>s+1;int n=strlen(s+1);
    b[0]=1;//
    for(int i=1;i<=n;i++)
    {
      b[i]=b[i-1]*base;//
      h1[i]=h1[i-1]*base+(int)p[i];
      h2[i]=h2[i-1]*base+(int)s[i];
    }
    int ans=0;
    for(int i=1;i+m-1<=n;i++)
    {//
      if(getHash(h1,1,m)==getHash(h2,i,i+m-1))ans++;
    }
    cout<<ans<<'\n';
    return 0;
}