CF EDU 126 C - Water the Trees

C - Water the Trees

二分

因为奇数天 +1， 偶数天 +2，所以找到最大的 $h[i]$ 记为 maxn，最后的高度只能在 maxn, maxn + 1 中，因为如果答案为 maxn + 2，则可以去掉一些操作，使最大高度为 maxn

二分答案即可

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>

using namespace std;
typedef long long ll;
const int N = 3e5 + 10;
ll h[N];
int n;

bool check(ll x, ll maxn)
{
	ll odd = (x + 1) / 2;
	ll even = x / 2;
	ll t1 = 0, t2 = 0;
	for (int i = 1; i <= n; i++)
	{
		ll t = maxn - h[i];
		t1 += t % 2;
		t2 += t / 2;
	}
	if (odd < t1)
		return false;
	if (odd + even * 2 < t1 + t2 * 2)
		return false;
	return true;
}

int main()
{
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	int T;
	cin >> T;
	while(T--)
	{
		cin >> n;
		ll maxn = 0;
		for (int i = 1; i <= n; i++)
			cin >> h[i], maxn = max(maxn, h[i]);
		ll l = -1, r = 1e18;
		while(l + 1 != r)
		{
			ll mid = l + r >> 1;
			if (check(mid, maxn))
				r = mid;
			else
				l = mid;
		}
		ll ans = r;
		
		l = -1, r = 1e18;
		while(l + 1 != r)
		{
			ll mid = l + r >> 1;
			if (check(mid, maxn + 1))
				r = mid;
			else
				l = mid;
		}
		ans = min(ans, r);
		cout << ans << endl;
	}
	return 0;
}