Submission #316400

#	Time	Username	Problem	Language	Result	Execution time	Memory
316400		nouvo25	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	33 ms	14208 KiB

kangaroo

#include <bits/stdc++.h>
#define fi first
#define se second
#define ll long long
#define io ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)

using namespace std;

const int MOD = 1e9 + 7, MAXN = 2007;

int dp[MAXN][MAXN] = {}, n, cs, cf;

void add(int &a, const int &b)
{
	a += b;
	if (a >= MOD) a -= MOD;
}

int main()
{
//	freopen("test.INP","r",	stdin);
	io;
	cin >> n >> cs >> cf;
	
	dp[0][0] = 1;
	for (int i = 1; i < n; ++i)
	{
		for (int j = 0; j <= i; ++j)
		{
			if (i == cs || i == cf)
			{
				add(dp[i][j], dp[i - 1][j]);
				add(dp[i][j], 1LL*(j + 1)*dp[i - 1][j + 1] % MOD);
			}else
			{
				add(dp[i][j], 1LL*j*(j + 1)*dp[i - 1][j + 1] % MOD);
				if (j) add(dp[i][j], dp[i - 1][j - 1]);
				if (i > cs) add(dp[i][j], 1LL*(j + 1)*dp[i - 1][j + 1] % MOD);
				if (i > cf) add(dp[i][j], 1LL*(j + 1)*dp[i - 1][j + 1] % MOD);
			}
		}
	}

	cout << dp[n - 1][0];
	return 0;
}

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