Submission #463503

#	Time	Username	Problem	Language	Result	Execution time	Memory
463503		huukhang	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	31 ms	31784 KiB

kangaroo

/*
						   Khangnh's code

“You can either experience the pain of discipline or the pain of regret. 
						The choice is yours.”
*/

// - Only when necessary :d
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("avx,avx2,fma")

#include <bits/stdc++.h>
using namespace std;

#define fileopen(a, b) freopen(((string)a + ".inp").c_str(), "r", stdin); freopen(((string)b + ".out").c_str(), "w", stdout);

#define ll long long
// #define int long long
#define ld long double
#define fi first
#define se second
#define pb push_back
#define pf push_front
#define pob pop_back
#define pof pop_front
#define eb emplace_back
typedef pair<int, int> pii;

const ll mod = 1e9 + 7;
const ll inf = 1e9 + 7;
const double eps = 1e-9;

inline void sadd(ll &x, const ll &y) {x = (x + y)%mod;}
inline ll mmul(const ll &x, const ll &y) {return (x*y)%mod;}

int n, s, e;
ll dp[2005][2005];

void solve() {
	cin >> n >> s >> e;

	memset(dp, 0, sizeof(dp));
	dp[1][1] = 1;

	for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= i; ++j) {
			if (i + 1 == s || i + 1 == e) {
				sadd(dp[i + 1][j + 1], dp[i][j]);
				sadd(dp[i + 1][j], dp[i][j]);
			} else {
				sadd(dp[i + 1][j - 1], mmul(dp[i][j], j - 1));
				sadd(dp[i + 1][j + 1], mmul(dp[i][j], j + 1 - (i + 1 > s) - (i + 1 > e)));
			}
		}
	}

	cout << dp[n][1];
}

signed main() {
	#ifdef LOCAL
		fileopen("input", "output");
		auto start = clock();
	#endif
	#ifndef LOCAL
//		fileopen("LAH", "LAH");
	#endif
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	int test = 1;
//	cin >> test;
	for (int tc = 1; tc <= test; ++tc) solve();
	#ifdef LOCAL
		auto end = clock();
		cout << "\n\nExecution time : " << double(end - start)/CLOCKS_PER_SEC << "[s]";
	#endif
	return 0;
}

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