結果

提出番号	1202
提出者	square1001
言語	C++
提出日時	2018-05-18 21:10:10
問題名	(51)boat(ボート)
結果	AC
点数	100%

---

テストケース

ソースコード

#include <iostream>
#include <algorithm>
using namespace std;
const int mod = 1000000007;
int n, c, a[509], b[509], x[1009], inv[509], comb[1009][509], dp[509][1009];
int main() {
	cin >> n;
	for (int i = 0; i < n; ++i) {
		cin >> a[i] >> b[i];
		x[i] = a[i];
		x[i + n] = ++b[i];
	}
	sort(x, x + 2 * n);
	c = unique(x, x + 2 * n) - x;
	for (int i = 0; i < n; ++i) {
		a[i] = lower_bound(x, x + c, a[i]) - x;
		b[i] = lower_bound(x, x + c, b[i]) - x;
	}
	inv[1] = 1;
	for (int i = 2; i <= n; ++i) {
		inv[i] = 1LL * inv[mod % i] * (mod - mod / i) % mod;
	}
	for (int i = 0; i < c - 1; ++i) {
		int way = 1;
		for (int j = 1; j <= n; ++j) {
			way = 1LL * way * (x[i + 1] - x[i] + j - 1) % mod * inv[j] % mod;
			comb[i][j] = way;
			if (comb[i][j] >= mod) comb[i][j] -= mod;
		}
	}
	int ans = 0;
	for (int i = 0; i < n; ++i) {
		for (int j = a[i]; j < b[i]; ++j) {
			int num = 0;
			for (int k = i - 1; k >= 0; --k) {
				if (a[k + 1] <= j && j < b[k + 1]) ++num;
				dp[i][j + 1] = (dp[i][j + 1] + 1LL * comb[j][num] * dp[k][j]) % mod;
			}
			if (a[0] <= j && j < b[0]) ++num;
			dp[i][j + 1] += comb[j][num];
			if (dp[i][j + 1] >= mod) dp[i][j + 1] -= mod;
		}
		for (int j = 0; j < c - 1; ++j) {
			dp[i][j + 1] += dp[i][j];
			if (dp[i][j + 1] >= mod) dp[i][j + 1] -= mod;
		}
		ans += dp[i][c - 1];
		if (ans >= mod) ans -= mod;
	}
	cout << ans << '\n';
	return 0;
}