Submission #243539

#	Time	Username	Problem	Language	Result	Execution time	Memory
243539		tonowak	Kangaroo (CEOI16_kangaroo)	C++17	0 / 100	5 ms	384 KiB

kangaroo

#include <bits/stdc++.h> // Tomasz Nowak
using namespace std;     // XIII LO Szczecin
using LL = long long;    // Poland
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define REP(i, n) FOR(i, 0, (n) - 1)
template<class T> int size(T &&x) {
	return int(x.size());
}
template<class A, class B> ostream& operator<<(ostream &out, const pair<A, B> &p) {
	return out << '(' << p.first << ", " << p.second << ')';
}
template<class T> auto operator<<(ostream &out, T &&x) -> decltype(x.begin(), out) {
	out << '{';
	for(auto it = x.begin(); it != x.end(); ++it)
		out << *it << (it == prev(x.end()) ? "" : ", ");
	return out << '}';
}
void dump() {}
template<class T, class... Args> void dump(T &&x, Args... args) {
	cerr << x << ";  ";
	dump(args...);
}
#ifdef DEBUG
  struct Nl{~Nl(){cerr << '\n';}};
# define debug(x...) cerr << (strcmp(#x, "") ? #x ":  " : ""), dump(x), Nl(), cerr << ""
#else
# define debug(...) 0 && cerr
#endif
mt19937_64 rng(0);
int rd(int l, int r) {
	return uniform_int_distribution<int>(l, r)(rng);
}
// end of templates

constexpr int mod = int(1e9) + 7;

int add(int a, int b) {
	a += b;
	if(a >= mod)
		a -= mod;
	return a;
}

int mul(int a, int b) {
	return int(a * LL(b) % mod);
}

int& add_to(int &a, int b) {
	return a = add(a, b);
}

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	int n, start, end;
	cin >> n >> start >> end;

	vector<vector<array<int, 3>>> dp(n + 1, vector<array<int, 3>>(n, array<int, 3>{{0, 0, 0}}));
	dp[0][0][0] = 1;

	auto choose2 = [&](int cnt) {
		return int((cnt * LL(cnt - 1) / 2) % mod);
	};

	FOR(i, 1, n)
		FOR(open, 0, n - 1) {
			if(i == start or i == end) {
				add_to(dp[i][open][1], dp[i - 1][open][0]);
				add_to(dp[i][open][2], dp[i - 1][open][1]);
				if(open + 1 < n) {
					add_to(dp[i][open][1], dp[i - 1][open + 1][0]);
					add_to(dp[i][open][2], dp[i - 1][open + 1][1]);
				}
			}
			else {
				if(open + 1 < n) {
					add_to(dp[i][open][0], mul(dp[i - 1][open + 1][0], choose2(open + 1)));
					add_to(dp[i][open][1], mul(dp[i - 1][open + 1][1], choose2(open + 1)));
					add_to(dp[i][open][2], mul(dp[i - 1][open + 1][2], choose2(open + 1)));
					add_to(dp[i][open][0], dp[i - 1][open][2]);
				}
				if(open >= 1) {
					add_to(dp[i][open][0], dp[i - 1][open - 1][0]);
					add_to(dp[i][open][1], dp[i - 1][open - 1][1]);
					add_to(dp[i][open][2], dp[i - 1][open - 1][2]);
				}
			}
		}
	FOR(i, 1, n)
		FOR(open, 0, n - 1)
			debug(i, open, dp[i][open]);
	cout << dp[n][0][0] << '\n';
}

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