Codeforces Round 616 (Div. 2)
B
Array Sharpening
Codeforces
1300
原题
← AC →
翻译中…

You're given an array $a_1, \ldots, a_n$ of $n$ non-negative integers.

翻译中…

Let's call it sharpened if and only if there exists an integer $1 \le k \le n$ such that $a_1 \lt a_2 \lt \ldots \lt a_k$ and $a_k \gt a_{k+1} \gt \ldots \gt a_n$. In particular, any strictly increasing or strictly decreasing array is sharpened. For example:

翻译中…
  • The arrays $[4]$, $[0, 1]$, $[12, 10, 8]$ and $[3, 11, 15, 9, 7, 4]$ are sharpened;
  • The arrays $[2, 8, 2, 8, 6, 5]$, $[0, 1, 1, 0]$ and $[2, 5, 6, 9, 8, 8]$ are not sharpened.
翻译中…

You can do the following operation as many times as you want: choose any strictly positive element of the array, and decrease it by one. Formally, you can choose any $i$ ($1 \le i \le n$) such that $a_i \gt 0$ and assign $a_i := a_i - 1$.

翻译中…

Tell if it's possible to make the given array sharpened using some number (possibly zero) of these operations.

翻译中…

Input

翻译中…

The input consists of multiple test cases. The first line contains a single integer $t$ ($1 \le t \le 15\ 000$)  — the number of test cases. The description of the test cases follows.

翻译中…

The first line of each test case contains a single integer $n$ ($1 \le n \le 3 \cdot 10^5$).

翻译中…

The second line of each test case contains a sequence of $n$ non-negative integers $a_1, \ldots, a_n$ ($0 \le a_i \le 10^9$).

翻译中…

It is guaranteed that the sum of $n$ over all test cases does not exceed $3 \cdot 10^5$.

翻译中…

Output

翻译中…

For each test case, output a single line containing "Yes" (without quotes) if it's possible to make the given array sharpened using the described operations, or "No" (without quotes) otherwise.

翻译中…

Note

翻译中…

In the first and the second test case of the first test, the given array is already sharpened.

翻译中…

In the third test case of the first test, we can transform the array into $[3, 11, 15, 9, 7, 4]$ (decrease the first element $97$ times and decrease the last element $4$ times). It is sharpened because $3 \lt 11 \lt 15$ and $15 \gt 9 \gt 7 \gt 4$.

翻译中…

In the fourth test case of the first test, it's impossible to make the given array sharpened.

翻译中…

样例

Input #1
10
1
248618
3
12 10 8
6
100 11 15 9 7 8
4
0 1 1 0
2
0 0
2
0 1
2
1 0
2
1 1
3
0 1 0
3
1 0 1
Output #1
Yes
Yes
Yes
No
No
Yes
Yes
Yes
Yes
No
InputCopy OutputCopy
题目信息
题号
1291B
时间限制
1 s
内存限制
256 MB
标签
贪心
模拟

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。