P2527 [SHOI2001]Panda的烦恼

考虑优先队列广搜，第 $k$ 次出队的即为答案。注意需要去重。复杂度 $O(nk \log (nk))$，开 O2 可过，注意不要使用 long long，会 MLE。

#include <iostream>
#include <queue>
#include <cmath>
#include <algorithm>
#include <vector>
using namespace std;

const int N = 105;

#define ll int

priority_queue<ll, vector<ll>, greater<ll> > q;
int n, k;
int a[N];

ll bfs()
{
	int cnt = 0;
	ll last = 0;
	sort(a + 1, a + n + 1);
	for (int i = 1; i <= n; i++) q.push(a[i]);
	while (q.size())
	{
		ll p = q.top();
		q.pop();
		if (last == p) continue;
		last = p;
		if (++cnt == k) return p;
		for (int i = 1; i <= n; i++)
		{
			if (1ll * p * a[i] > (long long)2e9) break;
			q.push(p * a[i]);
		}
	}
}

int main()
{
	ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
	cin >> n >> k;
	//k++;
	for (int i = 1; i <= n; i++) cin >> a[i];
	cout << bfs() << "\n";
	return 0;
}