用字符串哈希做的，结果发现标签是 KMP……？

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

const int N = 1e6 + 10, B = 131;
multiset<ull> st;
ull p[N], h1[N], h2[N];

ull myHash(string s, ull h[]) {
	for (int i = 1; i <= s.length(); ++i) {
		h[i] = h[i - 1] * B + s[i - 1];
	}
	return h[s.length()];
}

ull subHash(ull h[], int l, int r) {
	return h[r] - h[l - 1] * p[r - l + 1];
}

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] * B;
	}
	int l;
	string s;
	cin >> l >> s;
	myHash(s, h1);
	for (int i = 1; i <= l; i++) {
		ull t = subHash(h1, 1, i);
		bool flag = true;
		for (int j = 1; j <= l / i; j++) {
			int x = i * (j - 1) + 1, y = i * j;
			if (subHash(h1, x, y) != t) {
				flag = false;
				break;
			}
		}
		if (!flag) continue;
		if (l % i != 0) {
			ull t1 = subHash(h1, l - l % i + 1, l);
			ull t2 = subHash(h1, 1, l % i);
			if (t1 == t2) {
				cout << i << endl;
				return 0;
			}
		} else {
			cout << i << endl;
			return 0;
		}
	}
	return 0;
}