Codeforces Round 906 (Div. 1)
B
Doremy's Connecting Plan
Codeforces
1700
原题
← AC1 →
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Doremy lives in a country consisting of $n$ cities numbered from $1$ to $n$, with $a_i$ people living in the $i$-th city. It can be modeled as an undirected graph with $n$ nodes.

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Initially, there are no edges in the graph. Now Doremy wants to make the graph connected.

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To do this, she can add an edge between $i$ and $j$ if

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$$ \sum_{k \in S} a_k \ge i\cdot j \cdot c, $$

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where $S$ is the set of all the nodes that are currently in the same connected component of either $i$ or $j$, and $c$ is a given constant.

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Can Doremy make the graph connected?

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Two nodes $(i, j)$ are in the same connected component if there exists a path from $i$ to $j$. A graph is connected if all its nodes are in the same connected component.

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Input

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The input consists of multiple test cases. The first line contains a single integer $t$ ($1\le t\le 10^4$) — the number of test cases. The description of the test cases follows.

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The first line contains two integers $n$, $c$ ($2\le n\le 2\cdot 10^5$, $1 \le c \le 10^6$) — the number of nodes and the constant.

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The second line of each test case contains $ n $ integers $ a_1,a_2,\ldots,a_n $ ($0 \le a_i \le 10^{12}$) — the number of people living in the $i$-th city.

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It is guaranteed that the sum of $n$ over all test cases does not exceed $2\cdot 10^5$.

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Output

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For each test case, print "YES" (without quotes), if it is possible to make the graph connected, and "NO" (without quotes) otherwise.

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You can print letters in any case (upper or lower).

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Note

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In the first test case, Doremy can add edges in the following order:

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  1. Add $(1,2)$. This operation is valid because $a_1 + a_2 = 20 \ge i\cdot j \cdot c = 20$.
  2. Add $(1,3)$. This operation is valid because $a_1 + a_2 + a_3 = 35 \ge i \cdot j \cdot c = 30$.
  3. Add $(1,4)$. This operation is valid because $a_1 + a_2 + a_3 + a_4 = 45 \ge i \cdot j \cdot c = 40$.
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In the second test case, Doremy can add edge $(1,2)$ because $a_1 + a_2 =2 \ge 1 \cdot 2 \cdot 1$. After that, the graph is connected.

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In the third test case, Doremy can add edges in the order $(5,4)$, $(5,3)$, $(5,2)$ and $(5,1)$.

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In the fourth test case, Doremy cannot add any edge at all.

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样例

Input #1
7
4 10
0 20 15 10
2 1
1 1
5 1
0 1 0 4 199
5 2
1 1 3 1 1
5 5
5 6 1 10 2
5 1000000
1000000000000 1000000000000 1000000000000 1000000000000 1000000000000
3 1
0 0 2
Output #1
Yes
Yes
Yes
No
No
Yes
No
InputCopy OutputCopy
题目信息
题号
1889B
时间限制
1 s
内存限制
256 MB
标签
构造
贪心
数学
排序

题面与样例版权归 Codeforces 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。