Leetcode 314 Binary Tree Vertical Order Traversa

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;