Submission #1015062

#	Time	Username	Problem	Language	Result	Execution time	Memory
1015062		yellowtoad	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	89 ms	94628 KiB

kangaroo

#include <iostream>
using namespace std;

const long long mod = 1e9+7;
long long n, st, ed, dp[2010][2010][3];

int main() {
	cin >> n >> st >> ed;
	if ((st == 1) || (ed == 1)) dp[1][1][1] = 1;
	else dp[1][1][0] = 1;
	for (int i = 2; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			for (int k = 0; k < 3; k++) {
				if ((i == st) || (i == ed)) {
					if (k > 0) {
						if ((k < 2) || (i == n) || (j > 1)) (dp[i][j][k] += dp[i-1][j][k-1]) %= mod;
						(dp[i][j][k] += dp[i-1][j-1][k-1]) %= mod;
					}
				} else {
					(dp[i][j][k] += dp[i-1][j-1][k]*(j-k)) %= mod;
					(dp[i][j][k] += dp[i-1][j+1][k]*j) %= mod;
				}
			}
		}
	}
	cout << dp[n][1][2] << endl;
}

• Subtask 1: 6 / 6
• Subtask 2: 30 / 30
• Subtask 3: 15 / 15
• Subtask 4: 49 / 49