Submission #866467

#	Time	Username	Problem	Language	Result	Execution time	Memory
866467		MisterReaper	A Huge Tower (CEOI10_tower)	C++17	45 / 100	2379 ms	262144 KiB

tower

//author: Ahmet Alp Orakci
#include <bits/stdc++.h>
using namespace std;
using i64 = long long;

const int MOD = 1E9 + 9;

int dp[21][1 << 21];
int arr[21];

#define ONLINE_JUDGE
void solve() {
	memset(dp, -1, sizeof(dp));
	
	int n, d;
	cin >> n >> d;
	for(int i = 0; i < n; i++)
		cin >> arr[i];

	function <int(int, int)> f = [&](int last, int mask) -> int {
		if(mask == (1 << n) -1)
			return 1;
		
		if(dp[last][mask] != -1)
			return dp[last][mask];

		int res = 0;
		for(int i = 0; i < n; i++) {
			if(!(mask & (1 << i)) && (arr[i] <= d + arr[last])) {
				(res += f(i, mask | (1 << i))) %= MOD;
			}
		}

		assert(res >= 0);
		return dp[last][mask] = res;
	};

	int res = 0;
	for(int i = 0; i < n; i++) {
		(res += f(i, (1 << i))) %= MOD;
	}

	cout << res;
	
	return;
}

signed main() {
	#ifndef ONLINE_JUDGE
		freopen(".in", "r", stdin);
		freopen(".out", "w", stdout);
	#endif

	ios_base::sync_with_stdio(false);
	cin.tie(NULL); cout.tie(NULL);

	int t = 1; //cin >> t;
	for(int i = 1; i <= t; i++) {
		solve();
	}

	return 0;
}

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