Submission #125568

#	Time	Username	Problem	Language	Result	Execution time	Memory
125568		tutis	Kangaroo (CEOI16_kangaroo)	C++17	51 / 100	535 ms	524292 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++)
		{
			for (int b = 1; b <= n; b++)
			{
				L[n][a][b] = 0;
				R[n][a][b] = 0;
				if (a == b)
					continue;
				if (n == 2)
				{
					if (a > b)
					{
						L[n][a][b] = 1;
					}
					if (a < b)
					{
						R[n][a][b] = 1;
					}
				}
				else
				{
					for (int c = 1; c <= n; c++)
					{
						if (c > b)
						{
							L[n][a][b] += R[n - 1][a - (a > b)][c - (c > b)];
						}
						if (c < b)
						{
							R[n][a][b] += L[n - 1][a - (a > b)][c - (c > b)];
						}
					}
				}
				L[n][a][b] %= modulo;
				R[n][a][b] %= modulo;
			}
		}
	}
	ll ret = L[N][A][B] + R[N][A][B];
	ret %= modulo;
	return ret;
}
ll faster(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;
}
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