Objective: – Given a binary tree, print it in Bottom View of it.
What is Bottom View: Bottom view means when you look the tree from the bottom the nodes you will see will be called the bottom view of the tree. See the example below.
This Approach is quite similar to the – Print the Binary Tree in Vertical Order Path.
and Print The Top View of a Binary Tree. Just modified the code so that it will print only the last element it will encounter in the vertical order. That will be the bottom view.
How will you know that you are visiting the last node at every level(Vertically)?
- Take a variable called level, whenever you go left, do level++ AND whenever you go right do level–.
- With step above we have separated out the levels vertically.
- Now you need to store the elements of each level, so create a TreeMap and the (key,value) pair will be (level,element at that level).
- Now all we need to do the level order traversal and store only recent visited node at each level(vertically), this way you will be storing only the last element at each level.
- We will use simple queue technique for level order traversal or BFS.
- we will create a class QueuePack, this will store the objects containing node and its level.
- At the end traverse through TreeMap and print all the values in it, it will be the bottom view of a tree.
- See the code for better understanding.
Output: 4 6 5 7 8