Submission #556963

#	Time	Username	Problem	Language	Result	Execution time	Memory
556963		hollwo_pelw	Boat (APIO16_boat)	C++17	100 / 100	300 ms	2376 KiB

boat

#include <bits/stdc++.h>
using namespace std;

const int N = 505, mod = 1e9 + 7;

int n, m, a[N], b[N], cnt[N * 2], dp[N * 2][N], inv[N];
vector<int> v, f;

signed main(){
	cin.tie(0), cout.tie(0) -> sync_with_stdio(0);
	cin >> n;
	for (int i = 1; i <= n; i++)
		cin >> a[i] >> b[i], b[i] ++;

	inv[1] = 1;
	for (int i = 2; i <= n; i++)
		inv[i] = mod - 1ll * (mod / i) * inv[mod % i] % mod;

	for (int i = 1; i <= n; i++)
		v.push_back(a[i]), v.push_back(b[i]);

	sort(v.begin(), v.end());
	v.erase(unique(v.begin(), v.end()), v.end());

	f.resize(m = v.size() - 1);
	for (int i = 1; i < (int) v.size(); i++)
		f[i - 1] = v[i] - v[i - 1];
	
	for (int i = 1; i <= n; i++) {
		int l = lower_bound(v.begin(), v.end(), a[i]) - v.begin(), r = lower_bound(v.begin(), v.end(), b[i]) - v.begin(), cur = 1;

		for (int j = 0; j < l; j++) {
			for (int k = cnt[j]; k; k--)
				if ((cur += dp[j][k]) >= mod)
					cur -= mod;
		}

		for (int j = l; j < r; j++) {
			int nxt = cur;
			for (int k = cnt[j]; k; k--) {
				if ((nxt += dp[j][k]) >= mod)
					nxt -= mod;
				dp[j][k + 1] += 1ll * dp[j][k] * (f[j] - k) % mod * inv[k + 1] % mod;
				if (dp[j][k + 1] >= mod) dp[j][k + 1] -= mod;
			}
			++ cnt[j];

			dp[j][1] += 1ll * cur * f[j] % mod;
			if (dp[j][1] >= mod) dp[j][1] -= mod;

			swap(nxt, cur);
		}
	}

	int res = 0;
	for (int j = 0; j < m; j++)
		for (int k = 1; k <= cnt[j]; k++)
			if ((res += dp[j][k]) >= mod)
				res -= mod;
	cout << res << '\n';
}

• Subtask 1: 9 / 9
• Subtask 2: 22 / 22
• Subtask 3: 27 / 27
• Subtask 4: 42 / 42