Submission #125563

#	Time	Username	Problem	Language	Result	Execution time	Memory
125563		tutis	Kangaroo (CEOI16_kangaroo)	C++17	36 / 100	2063 ms	18572 KiB

kangaroo

/*input
4 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;
int sgn(ll x)
{
	if (x < 0)
		return -1;
	if (x > 0)
		return 1;
	return 0;
}
map<tuple<int, int, int, int>, ll>M;
ll f(int n, int a, int b, int s)
{
	if (a == b)
		return 0;
	if (M.count(make_tuple(n, a, b, s)))
		return M[make_tuple(n, a, b, s)];
	if (n == 2)
	{
		if (sgn(b - a) != s)
			return 0;
		else
			return 1;
	}
	ll ret = 0;
	for (int c = 1; c <= n; c++)
	{
		if (sgn(b - c) == s)
		{
			ret += f(n - 1, a - (a > b), c - (c > b), -s);
		}
	}
	ret %= modulo;
	return M[make_tuple(n, a, b, s)] = ret;
}
int main()
{
	int n, a, b;
	cin >> n >> a >> b;
	ll ans = f(n, a, b, 1) + f(n, a, b, -1);
	ans %= modulo;
	cout << ans << "\n";
}

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