杭電多校補題

1001.迴圈位移

題意：

定義一個字串[A] 它代表著是一個迴圈位移的字串. 給你T組資料，字串A, B.問你在B字串中有多少子串是[A]

Code:

#include<bits/stdc++.h>
    
using namespace std;
typedef unsigned long long ull; 
const int N = 1048580 * 2; 
const int P = 131;
ull p[N], h1[N], h2[N];

void solve() {
    string a, b;
    cin >> a >> b;
    int n = a.size(), m = b.size();
    a = a + a;
    for (int i = 0; i < (n << 1); i++) {
        h1[i + 1] = h1[i] * P + a[i]; 
    }
    for (int i = 0; i < m; i++) {
        h2[i + 1] = h2[i] * P + b[i]; 
    }
    map <ull, int> mp;
    for (int i = 0; i < n; i++) {
        mp[h1[i + n] - h1[i] * p[n]]++;
    }
    int ans = 0;
    for (int i = 0; i <= m - n; i++) {
        ans += mp[h2[i + n] - h2[i] * p[n]];
    }
    cout << ans << '\n';
}
    
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    p[0] = 1;
    for (int i = 1; i < N; i++) {
        p[i] = p[i - 1] * P;
    }
    int _; cin >> _;
    while(_--) solve();
    return 0;
}