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Grokking the Coding Interview Patterns in C++

Binary Tree Zigzag Level Order Traversal

Explore how to implement a zigzag level order traversal on a binary tree. Understand the alternating left-right traversal pattern for each level and learn to apply breadth-first search strategies to solve this common interview problem efficiently.

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Statement

Given a binary tree, return its zigzag level order traversal. The zigzag level order traversal corresponds to traversing nodes from left to right for one level, and then right to left for the next level, and so on, reversing direction after every level.

Constraints:

  • The number of nodes in the tree is in the range 00 to 500500.

  • −100≤-100 \leq node.data ≤100\leq 100

Examples

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:

Binary Tree Zigzag Level Order Traversal

1.

What will be the zigzag level order traversal of the following tree?

[0, 2, 4, 1, NULL, 3, -1, 5, 1, NULL, 6, NULL, 8]

A.

[[0], [2, 4] , [1, NULL, 3, -1], [5, 1, NULL, 6, NULL, 8]]

B.

[[0], [4, 2], [1, 3, -1], [8, 6, 1, 5]]

C.

[0, 4, 2, 1, 3, -1, 8, 6, 1, 5]

D.

[NULL]

1 / 2

Figure it out!

Here’s 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.
1
2
3
4
5

Try it yourself

Implement your solution in ZigZagLevelOrderTraversal.cpp in the coding playground below. We’ve provided some useful code templates in the other file that you may build on and use to solve this problem.

C++
usercode > ZigZagLevelOrderTraversal.cpp
typedef TreeNode<int>* NodePtr;
vector<vector<int>> ZigzagLevelOrder(TreeNode<int>* root){
    // Replace this placeholder return statement with your code
    return {};
}
Binary Tree Zigzag Level Order Traversal