This question is nothing fancy, just need to get the position that the root should be. and the length for the whole array
The idea is from here.
http://www.shuatiblog.com/blog/2014/12/17/Print-Binary-Tree-Vertically/
and use these two sentence to get the root position and the length of the array.
int rootIndex = 0 - range[0];
int columns = range[1] - range[0] + 1;