Solution
Approach 1: Greedy
Intuition
If x
is currently the array element with the least absolute value, it must pair with 2*x
, as there does not exist any other x/2
to pair with it.
Algorithm
Let's try to (virtually) "write" the final reordered array.
Let's check elements in order of absolute value. When we check an element x
and it isn't used, it must pair with 2*x
. We will attempt to write x, 2x
 if we can't, then the answer is false
. If we write everything, the answer is true
.
To keep track of what we have not yet written, we will store it in a count
.
Complexity Analysis

Time Complexity: , where is the length of
A
. 
Space Complexity: .
Analysis written by: @awice.