CF1760D.Challenging Valleys

You are given an array $a[0 \dots n-1]$ of $n$ integers. This array is called a "valley" if there exists exactly one subarray $a[l \dots r]$ such that:

• $0 \le l \le r \le n-1$,
• $a_l = a_{l+1} = a_{l+2} = \dots = a_r$,
• $l = 0$ or $a_{l-1} \gt a_{l}$,
• $r = n-1$ or $a_r \lt a_{r+1}$.

Here are three examples:

The first image shows the array [$3, 2, 2, 1, 2, 2, 3$], it is a valley because only subarray with indices $l=r=3$ satisfies the condition.

The second image shows the array [$1, 1, 1, 2, 3, 3, 4, 5, 6, 6, 6$], it is a valley because only subarray with indices $l=0, r=2$ satisfies the codition.

The third image shows the array [$1, 2, 3, 4, 3, 2, 1$], it is not a valley because two subarrays $l=r=0$ and $l=r=6$ that satisfy the condition.

You are asked whether the given array is a valley or not.

Note that we consider the array to be indexed from $0$.

给你一个包含 $n$ 个整数的数组 $a[0 \dots n-1]$。若该数组中恰好存在一个子数组 $a[l \dots r]$ 满足以下全部条件，则称该数组为“山谷”（valley）：

• $0 \le l \le r \le n-1$，
• $a_l = a_{l+1} = a_{l+2} = \dots = a_r$，
• $l = 0$ 或 $a_{l-1} \gt a_{l}$，
• $r = n-1$ 或 $a_r \lt a_{r+1}$。

以下是三个示例：

第一张图展示数组 $[3, 2, 2, 1, 2, 2, 3]$，它是一个山谷，因为仅下标满足 $l=r=3$ 的子数组符合上述条件。

第二张图展示数组 $[1, 1, 1, 2, 3, 3, 4, 5, 6, 6, 6]$，它是一个山谷，因为仅下标满足 $l=0,\, r=2$ 的子数组符合条件。

第三张图展示数组 $[1, 2, 3, 4, 3, 2, 1]$，它不是一个山谷，因为有两个子数组（$l=r=0$ 和 $l=r=6$）均满足条件。

你需要判断给定的数组是否为一个山谷。

注意：我们约定数组下标从 $0$ 开始。

The first line contains a single integer $t$ ($1 \leq t \leq 10^4$) — the number of test cases.

The first line of each test case contains a single integer $n$ ($1 \leq n \leq 2\cdot10^5$) — the length of the array.

The second line of each test case contains $n$ integers $a_i$ ($1 \leq a_i \leq 10^9$) — the elements of the array.

It is guaranteed that the sum of $n$ over all test cases is smaller than $2\cdot10^5$.

第一行包含一个整数 $t$（$1 \leq t \leq 10^4$）——测试用例的数量。

每个测试用例的第一行包含一个整数 $n$（$1 \leq n \leq 2\cdot10^5$）——数组的长度。

每个测试用例的第二行包含 $n$ 个整数 $a_i$（$1 \leq a_i \leq 10^9$）——数组的元素。

保证所有测试用例的 $n$ 之和小于 $2\cdot10^5$。

For each test case, output "YES" (without quotes) if the array is a valley, and "NO" (without quotes) otherwise.

You can output the answer in any case (for example, the strings "yEs", "yes", "Yes" and "YES" will be recognized as a positive answer).

对于每个测试用例，如果该数组是一个山谷数组（valley），则输出 "YES"（不带引号）；否则输出 "NO"（不带引号）。

你可以以任意大小写形式输出答案（例如，字符串 "yEs"、"yes"、"Yes" 和 "YES" 均被视为正确答案）。

The first three test cases are explained in the statement.

前三个测试用例在题目描述中已作解释。