Submission #125569

#	Time	Username	Problem	Language	Result	Execution time	Memory
125569		tutis	Kangaroo (CEOI16_kangaroo)	C++17	51 / 100	2077 ms	204600 KiB

kangaroo

/*input
10 2 3
*/
#pragma GCC optimize ("O3")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
const ll modulo = 1000000007;
ll fast(int N, int A, int B)
{
	ll L[N + 1][N + 1][N + 1];
	ll R[N + 1][N + 1][N + 1];
	for (int n = 2; n <= N; n++)
	{
		for (int a = 1; a <= n; a++)
		{
			L[n][a][0] = 0;
			R[n][a][0] = 0;
			for (int b = 1; b <= n; b++)
			{
				L[n][a][b] = L[n][a][b - 1];
				R[n][a][b] = R[n][a][b - 1];
				if (a == b)
					continue;
				if (n == 2)
				{
					if (a > b)
					{
						L[n][a][b] = 1;
					}
					if (a < b)
					{
						R[n][a][b] = 1;
					}
				}
				else
				{
					L[n][a][b] += R[n - 1][a - (a > b)][n - 1];
					L[n][a][b] -= R[n - 1][a - (a > b)][b - 1];
					R[n][a][b] += L[n - 1][a - (a > b)][b - 1];
				}
				L[n][a][b] %= modulo;
				R[n][a][b] %= modulo;
			}
		}
	}
	ll ret = L[N][A][B] - L[N][A][B - 1] + R[N][A][B] - R[N][A][B - 1];
	ret %= modulo;
	ret += modulo;
	ret %= modulo;
	return ret;
}
ll R(int n, int a, int b);
map<tuple<int, int, int>, int>LL;
ll L(int n, int a, int b)
{
	if (LL.count(make_tuple(n, a, b)))
		return LL[make_tuple(n, a, b)];
	if (b == 0)
		return 0;
	ll ret = L(n, a, b - 1);
	if (a == b)
		return LL[make_tuple(n, a, b)] = ret;
	if (n == 2)
	{
		if (a > b)
			ret++;
	}
	else
	{
		ret += R(n - 1, a - (a > b), n - 1);
		ret -= R(n - 1, a - (a > b), b - 1);
	}
	ret %= modulo;
	return LL[make_tuple(n, a, b)] = ret;
}
map<tuple<int, int, int>, int>RR;
ll R(int n, int a, int b)
{
	if (RR.count(make_tuple(n, a, b)))
		return RR[make_tuple(n, a, b)];
	if (b == 0)
		return 0;
	ll ret = R(n, a, b - 1);
	if (a == b)
		return RR[make_tuple(n, a, b)] = ret;
	if (n == 2)
	{
		if (a < b)
			ret++;
	}
	else
	{
		ret += L(n - 1, a - (a > b), b - 1);
	}
	ret %= modulo;
	return RR[make_tuple(n, a, b)] = ret;
}
ll faster(int N, int A, int B)
{
	ll ret = L(N, A, B) - L(N, A, B - 1) + R(N, A, B) - R(N, A, B - 1);
	ret %= modulo;
	ret += modulo;
	ret %= modulo;
	return ret;
}
int main()
{
	int n, a, b;
	cin >> n >> a >> b;
	//cout << fast(n, a, b) << "\n";
	cout << faster(n, a, b) << "\n";
}

• Subtask 1: 6 / 6
• Subtask 2: 30 / 30
• Subtask 3: 15 / 15
• Subtask 4: 0 / 49