Codeforces Round 724 (Div. 2) |
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Finished |
Uh oh! Ray lost his array yet again! However, Omkar might be able to help because he thinks he has found the OmkArray of Ray's array. The OmkArray of an array $$$a$$$ with elements $$$a_1, a_2, \ldots, a_{2k-1}$$$, is the array $$$b$$$ with elements $$$b_1, b_2, \ldots, b_{k}$$$ such that $$$b_i$$$ is equal to the median of $$$a_1, a_2, \ldots, a_{2i-1}$$$ for all $$$i$$$. Omkar has found an array $$$b$$$ of size $$$n$$$ ($$$1 \leq n \leq 2 \cdot 10^5$$$, $$$-10^9 \leq b_i \leq 10^9$$$). Given this array $$$b$$$, Ray wants to test Omkar's claim and see if $$$b$$$ actually is an OmkArray of some array $$$a$$$. Can you help Ray?
The median of a set of numbers $$$a_1, a_2, \ldots, a_{2i-1}$$$ is the number $$$c_{i}$$$ where $$$c_{1}, c_{2}, \ldots, c_{2i-1}$$$ represents $$$a_1, a_2, \ldots, a_{2i-1}$$$ sorted in nondecreasing order.
Each test contains multiple test cases. The first line contains a single integer $$$t$$$ ($$$1 \leq t \leq 10^4$$$) — the number of test cases. Description of the test cases follows.
The first line of each test case contains an integer $$$n$$$ ($$$1 \leq n \leq 2 \cdot 10^5$$$) — the length of the array $$$b$$$.
The second line contains $$$n$$$ integers $$$b_1, b_2, \ldots, b_n$$$ ($$$-10^9 \leq b_i \leq 10^9$$$) — the elements of $$$b$$$.
It is guaranteed the sum of $$$n$$$ across all test cases does not exceed $$$2 \cdot 10^5$$$.
For each test case, output one line containing YES if there exists an array $$$a$$$ such that $$$b_i$$$ is the median of $$$a_1, a_2, \dots, a_{2i-1}$$$ for all $$$i$$$, and NO otherwise. The case of letters in YES and NO do not matter (so yEs and No will also be accepted).
5 4 6 2 1 3 1 4 5 4 -8 5 6 -7 2 3 3 4 2 1 2 3
NO YES NO YES YES
5 8 -8 2 -6 -5 -4 3 3 2 7 1 1 3 1 0 -2 -1 7 6 12 8 6 2 6 10 6 5 1 2 3 6 7 5 1 3 4 3 0
NO YES NO NO NO
In the second case of the first sample, the array $$$[4]$$$ will generate an OmkArray of $$$[4]$$$, as the median of the first element is $$$4$$$.
In the fourth case of the first sample, the array $$$[3, 2, 5]$$$ will generate an OmkArray of $$$[3, 3]$$$, as the median of $$$3$$$ is $$$3$$$ and the median of $$$2, 3, 5$$$ is $$$3$$$.
In the fifth case of the first sample, the array $$$[2, 1, 0, 3, 4, 4, 3]$$$ will generate an OmkArray of $$$[2, 1, 2, 3]$$$ as
In the second case of the second sample, the array $$$[1, 0, 4, 3, 5, -2, -2, -2, -4, -3, -4, -1, 5]$$$ will generate an OmkArray of $$$[1, 1, 3, 1, 0, -2, -1]$$$, as
For all cases where the answer is NO, it can be proven that it is impossible to find an array $$$a$$$ such that $$$b$$$ is the OmkArray of $$$a$$$.
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