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Grokking the Coding Interview Patterns in Python

Vertical Order Traversal of a Binary Tree

Explore the vertical order traversal technique for binary trees, focusing on retrieving node values column by column from top to bottom. Understand how to handle nodes in the same row and column while implementing BFS traversal methods to solve this common coding interview problem efficiently.

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Statement

Find the vertical order traversal of a binary tree when the root of the binary tree is given. In other words, return the values of the nodes from top to bottom in each column, column by column from left to right. If there is more than one node in the same column and row, return the values from left to right.

Constraints:

  • The number of nodes in the tree is in the range [1, 500].
  • 0≤0 \leq Node.data ≤1000\leq 1000

Examples

In the slides below, the input parameter is a list that represents the level order traversal of the binary tree.

canvasAnimation-image
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Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Vertical Order Traversal of a Binary Tree

1.

What should be the output if the following tree is given as input?

tree = [25, 14, 35, -1, 15, null, 200, null, 10, null, null, 90, 350]

          __ 25 _ 
         |       |
      __ 14 _    35 _ 
     |       |       |
     -1 _    15   __ 200 _ 
         |       |        |
         10      90       350
A.

[[25], [14, 35], [-1, 15, 200], [10, 90, 350]]

B.

[[-1], [14, 10], [25, 15], [35, 90], [200], [350]]

C.

[[-1], [14], [10], [25], [15], [35], [90], [200], [350]]

D.

[[25, 14, -1], [10], [14, 15], [200, 90], [125, 35, 200, 350]]

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
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Try it yourself

Implement your solution in the following coding playground.

Python
usercode > main.py
# Definition for a binary tree node

# class TreeNode:

#     def __init__(self, data):

#         self.data = data

#         self.left = None

#         self.right = None



from ds_v1.BinaryTree.BinaryTree import TreeNode



def vertical_order(root):



    # Replace this placeholder return statament with your code

    return []
Vertical Order Traversal of a Binary Tree