Submission #657465

#	Time	Username	Problem	Language	Result	Execution time	Memory
657465		GusterGoose27	Kangaroo (CEOI16_kangaroo)	C++11	100 / 100	9 ms	12244 KiB

kangaroo

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int MOD = 1e9+7;
const int MAXN = 2001;
int dp[MAXN][MAXN];

int n, a, b;

int main() {
	ios_base::sync_with_stdio(false); cin.tie(NULL);
	cin >> n >> a >> b;
	a--; b--;
	dp[0][0] = 1;
	for (int i = 0; i < n; i++) {
		for (int j = 1; j <= min(i+1, n-i); j++) {
			if (i == a || i == b) {
				dp[i+1][j] = dp[i][j]+dp[i][j-1];
				dp[i+1][j] %= MOD;
			}
			else {
				dp[i+1][j] = ((ll) (j-(i >= a)-(i >= b))*dp[i][j-1]+(ll)j*dp[i][j+1]) % MOD;
			}
		}
	}
	cout << dp[n][1] << "\n";
}

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