Codeforces Global Round 22
B
Prefix Sum Addicts
Codeforces
1200
原题
← AC →
翻译中…

Suppose $a_1, a_2, \dots, a_n$ is a sorted integer sequence of length $n$ such that $a_1 \leq a_2 \leq \dots \leq a_n$.

翻译中…

For every $1 \leq i \leq n$, the prefix sum $s_i$ of the first $i$ terms $a_1, a_2, \dots, a_i$ is defined by $$ s_i = \sum_{k=1}^i a_k = a_1 + a_2 + \dots + a_i. $$

翻译中…

Now you are given the last $k$ terms of the prefix sums, which are $s_{n-k+1}, \dots, s_{n-1}, s_{n}$. Your task is to determine whether this is possible.

翻译中…

Formally, given $k$ integers $s_{n-k+1}, \dots, s_{n-1}, s_{n}$, the task is to check whether there is a sequence $a_1, a_2, \dots, a_n$ such that

翻译中…
  1. $a_1 \leq a_2 \leq \dots \leq a_n$, and
  2. $s_i = a_1 + a_2 + \dots + a_i$ for all $n-k+1 \leq i \leq n$.
翻译中…

Input

翻译中…

Each test contains multiple test cases. The first line contains an integer $t$ ($1 \leq t \leq 10^5$) — the number of test cases. The following lines contain the description of each test case.

翻译中…

The first line of each test case contains two integers $n$ ($1 \leq n \leq 10^5$) and $k$ ($1 \leq k \leq n$), indicating the length of the sequence $a$ and the number of terms of prefix sums, respectively.

翻译中…

The second line of each test case contains $k$ integers $s_{n-k+1}, \dots, s_{n-1}, s_{n}$ ($-10^9 \leq s_i \leq 10^9$ for every $n-k+1 \leq i \leq n$).

翻译中…

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

翻译中…

Output

翻译中…

For each test case, output "YES" (without quotes) if it is possible and "NO" (without quotes) otherwise.

翻译中…

You can output "YES" and "NO" in any case (for example, strings "yEs", "yes" and "Yes" will be recognized as a positive response).

翻译中…

Note

翻译中…

In the first test case, we have the only sequence $a = [1, 1, 1, 1, 1]$.

翻译中…

In the second test case, we can choose, for example, $a = [-3, -2, -1, 0, 1, 2, 3]$.

翻译中…

In the third test case, the prefix sums define the only sequence $a = [2, 1, 1]$, but it is not sorted.

翻译中…

In the fourth test case, it can be shown that there is no sequence with the given prefix sums.

翻译中…

样例

Input #1
4
5 5
1 2 3 4 5
7 4
-6 -5 -3 0
3 3
2 3 4
3 2
3 4
Output #1
Yes
Yes
No
No
InputCopy OutputCopy
题目信息
题号
1738B
时间限制
2 s
内存限制
512 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。