Submission #1059318

#	Time	Username	Problem	Language	Result	Execution time	Memory
1059318		TAhmed33	Kangaroo (CEOI16_kangaroo)	C++98	100 / 100	14 ms	16016 KiB

kangaroo

#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
int add (int a, int b) {
	a += b; if (a >= MOD) a -= MOD;
	return a;
}
int sub (int a, int b) {
	a -= b; if (a < 0) a += MOD;
	return a;
}
int mul (int a, int b) {
	return (a * 1ll * b) % MOD;
}
typedef long long ll;
int dp[2003][2003], n, s, t;
void solve () {
	cin >> n >> s >> t;
	dp[1][1] = 1;
	for (int i = 2; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			if (i == s || i == t) {
				dp[i][j] = add(dp[i - 1][j - 1], dp[i - 1][j]);
			} else {
				dp[i][j] = mul(dp[i - 1][j + 1], j);
				dp[i][j] = add(dp[i][j], mul(dp[i - 1][j - 1], j - (i > s) - (i > t)));
			}
		}
	}
	cout << dp[n][1] << '\n';
}		
signed main () {
	ios::sync_with_stdio(0); cin.tie(0);
	int tc = 1; //cin >> tc;
	while (tc--) solve();
}

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