滑动窗口来比较模式串与子串的哈希值

#include <iostream>
using namespace std;
typedef unsigned long long ULL;
const int N =1000010,P = 131;
ULL h1[N],h2[N],p[N];
int n,m;
char a[N],b[N];
ULL get(int l,int r)
{
    return h2[r] - h2[l-1] * p[r - l + 1];
}

int main()
{
    scanf("%d%s%d%s",&n,a+1,&m,b+1);
    p[0] = 1;
    for(int i = 1;i<=n;i++)
        h1[i] = h1[i-1]*P + a[i];
    for(int i = 1;i<=m;i++)
    {
        h2[i] = h2[i-1] * P + b[i];
        p[i] = p[i-1] * P;
    }
    for(int l = 1,r = n;r<=m;r++,l++)
    {
        if(get(l,r) == h1[n]) cout<<l-1<<" ";
    }
    return 0;
}