调了两年半了，求救。

#include <iostream>
#include <cstring>
using namespace std;
#define int long long
int mod = 1e9 + 7;

int qpow(int a, int b) {
	int ans = 1;
	while (b) {
		if (b % 2 == 1)
			ans = ans * a % mod;
		a = a * a % mod;
		b /= 2;
	}
	return ans % mod;
}
int jie[10000005], inv[10000005];

int C(int n, int m) {
	if (n < m || m < 0)
		return 0;
	return jie[n] * inv[n - m] % mod * inv[m] % mod;
}
int ans[10000005];
int a[6005], b[6005], f[6005], g[6005], vis[6005], nxt[6005];

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	jie[0] = 1;
	for (int i = 1; i <= 10000000; i++)
		jie[i] = jie[i - 1] * i % mod;
	inv[10000000] = qpow(jie[10000000], mod - 2);
	for (int i = 10000000 - 1; i >= 0; i--)
		inv[i] = inv[i + 1] * (i + 1) % mod;
	int t;
	t = 1;
	while (t--) {
		int n;
		cin >> n;
		for (int i = 1; i <= n; i++)
			cin >> a[i];
		for (int i = 1; i <= n; i++) {
			cin >> b[i];
			nxt[a[i]] = b[i];
		}
		f[0] = 1;
		int sum = 0;
		for (int i = 1; i <= n; i++)
			if (!vis[i]) {
				int du = 0;
				for (int x = i;; x = nxt[x]) {
					if (vis[x])
						break;
					vis[x] = 1;
					du++;
				}
				memset(g, 0, sizeof(g));
				if (du == 1) {
					g[0] = f[0];
					for (int i = 1; i <= sum + 1; i++)
						g[i] = f[i] + f[i - 1];
				} else {
					for (int i = 0; i <= sum; i++)
						for (int j = 0; j <= du; j++)
							g[i + j] += f[i] * (C(2 * du - j, j) + C(2 * du - j - 1, j - 1)) % mod, g[i + j] %= mod;
				}
				sum += du;
				for (int i = 0; i <= sum; i++)
					f[i] = g[i];
			}
		int ans = 0;
		for (int i = 0; i <= n; i++) {
			if (i % 2 == 0)
				ans += f[i] * jie[n - i] % mod;
			else
				ans -= f[i] * jie[n - i] % mod;
			ans = (ans % mod + mod) % mod;
		}
		cout << ans << endl;
		memset(f, 0, sizeof(f));
		memset(g, 0, sizeof(g));
		memset(nxt, 0, sizeof(nxt));
		memset(vis, 0, sizeof(vis));
	}
}