Given a binary tree, write a function to get the maximum width of the given tree. The width of a tree is the maximum width among all levels. The binary tree has the same structure as a full binary tree, but some nodes are null.
The width of one level is defined as the length between the end-nodes (the leftmost and right most non-null nodes in the level, where the
null nodes between the end-nodes are also counted into the length calculation.
Explanation:The maximum width existing in the fourth level with the length 8 (6,null,null,null,null,null,null,7).