1469C Building a Fence

題目

思路：每一次求取一個範圍，然後判斷之後的小方格是否滿足範圍。對於最後和第一個方格已經取定，需要特殊判斷，細節見程式碼。

Code:

#include<iostream>
#include<string>
#include<map>
#include<algorithm>
#include<memory.h>
#include<cmath>
#define pii pair<int,int>
#define FAST ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
using namespace std;
typedef long long ll;
const int Max = 1e6 + 5;
int Mod = 1e9 + 7;
int h[Max];
int main()
{
	int t;cin >> t;
	while (t--)
	{
		int n, k;cin >> n >> k;
		for (int i = 1;i <= n;i++)cin >> h[i];
		int l = h[1], r = h[1];
		int f = 1;
		for (int i = 2;i <= n-1;i++)
		{
			if (h[i] >= h[i - 1])
			{
				if (h[i] >= r + k) { f = 0;break; }
				l = h[i], r = min(h[i] + k-1, r + k - 1);
			}
			else
			{
				if (h[i] + k+k-1 <= l) { f = 0;break; }
				r = h[i] + k - 1, l = max(h[i], l - k + 1);
			}
		}
		if (h[n] + k <= l || h[n] >= r + k)f = 0;
		if (f)cout << "YES" << endl;
		else cout << "NO" << endl;

	}
}