KURUK14  GENIE SEQUENCE
A Genie Sequence is a sequence in which every element indicates the number of elements present before or after it. Given an array of numbers, find whether you can form a Genie sequence or not.
Input
First line contains a single integer T, the number of test cases. It is followed by T cases each of which contains two lines. First line of each test case contains a single integer N. The next line contains N integers separated by a single space.
Output
For each test case output a single line containing "YES
" (without quotes) if it is possible to form a genie sequence or "NO
" (without quotes) if it is not possible.
Constraints
1 <= T <= 20
2 <= N <= 1000
1 <= ai <= 1000
Example
Input: 1 4 1 3 3 2 Output: YES
Explanation for the test case:
The Genie sequence is {3, 1, 2, 3}. The first element '3' in the sequence indicates that three numbers are after it, the 2nd element '1' indicates that one number if before it, the 3rd element '2' indicates that two elements are before it and the last element indicates that three elements are before it. So the answer is YES.
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zemotacqy:
20170912 19:22:47
Using O(n) should be the main motive behind solving this question. 

mahilewets:
20170906 22:10:22
I do four walks through the sequence to determine the answer


vishesh197:
20170825 21:41:41
do it in O(n) just see backward and forwardshift for each element in array


code_aim:
20170822 18:25:13
Good Problem 

ankit1cool:
20170607 12:58:38
Try using O(n) ,don't go for O(n*n) i 

vengatesh15:
20170315 20:50:24
easy one done in O(n).. 

strangerx:
20170204 08:13:54
A O(n) solution exist using hashing . 

adi_1996:
20160702 21:32:24
easy


KD :
20160528 12:16:35
didn't read question carefully costed me 2 WA : ACfinally 

akshayvenkat:
20160523 07:45:26
O(n*n) works in c++ :D 
Added by:  785227 
Date:  20140131 
Time limit:  0.100s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  C CSHARP C++ 4.3.2 CPP C99 JAVA PERL PYTHON PYTHON3 
Resource:  Kurukshetra Onsite Programming Contest 