Submission #1793784

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Source Code Expand

#include <bits/stdc++.h>
#define mk make_pair
#define ll long long
using namespace std;
const int N = 400;
const int mod = 1e9 + 7;
int n, ans, g[N][N], f[N][N], s[N][N];
int a[N], b[N], pa[N], pb[N], cnt[N][N], ss[N], cnt_;
int main() {
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		pa[a[i]] = i;	
	}
	for (int i = 1; i <= n; i++) {
		cin >> b[i];
		pb[b[i]] = i;	
	}
	for (int i = 1; i <= n; i++) {
		ss[a[i]]++;
		if (ss[a[i]] == 1) cnt_++;
		for (int j = 1; j <= n; j++) {
			ss[b[j]]++;
			if (ss[b[j]] == 1) cnt_++;
			cnt[i][j] = cnt_;
		}
		for (int j = 1; j <= n; j++) {
			ss[b[j]]--;
			if (ss[b[j]] == 0) cnt_--;
		}
	}
	for (int i = 1; i <= n + 1; i++)
		for (int j = 1; j <= n + 1; j++)
			s[i][j] = 1;
	for (int i = 1; i <= n / 3; i++) {
		for (int j = 1; j <= n; j++) {
			for (int k = 1; k <= n; k++) {
				f[j][k] = 0;
				if (pa[b[k]] <= j) continue;
				if (pb[a[j]] <= k) continue;
				f[j][k] = (ll)(n - cnt[j][k] - (i - 1) * 3) * s[j + 1][k + 1] % mod;
			}
		}
		for (int j = 0; j <= n; j++)
			s[j][n + 1] = s[n + 1][j] = s[n + 1][n + 1] = 0;
		for (int j = n; j >= 1; j--) {
			for (int k = n; k >= 1; k--) {
				s[j][k] = f[j][k];
				(s[j][k] += (s[j + 1][k] + s[j][k + 1]) % mod) %= mod;
			}
		}
	}
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= n; j++) 
			(ans += f[i][j]) %= mod;
	g[0][0] = 1;
	for (int i = 0; i <= n / 3; i++) {
		for (int j = 0; j <= n; j++) {
			if (g[i][j] == 0) continue;
			if (i * 3 > j) (g[i][j + 1] += (ll)g[i][j] * (3 * i - j) % mod) %= mod;
			(g[i + 1][j + 1] += g[i][j]) %= mod;
		}
	}  
	cout << (ll)ans * g[n / 3][n] % mod << endl;
}

Submission Info

Judge Result