Hard problem's have benefits . Solve hard problem to learn a new something :)

If n==1 , The result should be 1 , because there are not any elements again in array,,Every number implies to length

There are alternative solutions for this problem without hashtable,We can do Vector Add numbers and Vector Add module for every number and every time , you must check , Are this number contains in this vector or not :) Hope it help

where c, d , e editorial for div 2 ??

GL for every one