DMOPC '22 Contest 1 P1 - Up-down Sequence
View as PDFAn up-down sequence is any sequence where the elements alternate between increasing and decreasing. Formally, a sequence  of 
 integers is considered to be an up-down sequence if for each 
, either 
 or 
. Given a sequence of 
 integers, some of which are forgotten, you must determine whether it is possible to replace each forgotten element with any integer so that the resulting sequence is an up-down sequence. To ensure the integrity of your solution, there will be 
 test cases.
Constraints
The sum of  over all test cases does not exceed 
.
Subtask 1 [20%]
Subtask 2 [80%]
No additional constraints.
Input Specification
The first line contains an integer , the number of test cases. The next 
 lines describe the test cases.
The first line of each test case contains a single integer .
The second line of each test case contains  integers 
. Forgotten elements are denoted by 
s in the sequence.
Output Specification
For each test case, output a single line containing YES if it is possible to make it an up-down sequence or NO otherwise.
Sample Input
4
7
1 0 2 5 3 0 2
5
3 0 1 2 3
4
1 0 0 1
3
6 6 0
Sample Output
YES
NO
YES
NO
Explanation for Sample
For the first test case, one may convert the sequence to .
For the third test case, one may convert the sequence to .
Comments