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Grokking the Coding Interview Patterns in C++

Vertical Order Traversal of a Binary Tree

Understand how to solve the vertical order traversal problem for binary trees by returning node values from top to bottom and left to right in each column. Practice implementing this using breadth-first search and improve your tree traversal skills.

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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.

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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.

C++
usercode > VerticalOrderTraversal.cpp
// Definition for a binary tree node
// template<class T>
// class TreeNode {
// public:
//     T data;
//     TreeNode<T>* left;
//     TreeNode<T>* right;
//     TreeNode(const T data) : data(data), left(nullptr), right(nullptr) {}
// };
std::vector<std::vector<int>> VerticalOrder(TreeNode<int> *root){
  // Replace this placeholder return statament with your code
  return {};
}
Vertical Order Traversal of a Binary Tree