Zigzag Level Order Traversal in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Zigzag Level Order Traversal in a binary tree?

It is a way to visit nodes level by level, but alternating the direction of traversal at each level. For example, left to right on one level, then right to left on the next.

beginner

Why do we use a queue in Zigzag Level Order Traversal?

A queue helps us visit nodes level by level in order. It stores nodes of the current level so we can process them before moving to the next level.

intermediate

How do we alternate the direction of traversal in Zigzag Level Order Traversal?

We use a flag or boolean variable that switches after each level. If true, we add nodes left to right; if false, we add nodes right to left.

intermediate

What data structure can help reverse the order of nodes at alternate levels efficiently?

A stack or reversing the array of nodes collected at a level can help reverse the order before adding to the result.

beginner

What is the time complexity of Zigzag Level Order Traversal?

The time complexity is O(n), where n is the number of nodes, because each node is visited exactly once.

In Zigzag Level Order Traversal, what data structure is primarily used to keep track of nodes at each level?

A Linked List

B Queue

C Hash Map

D Stack

A queue is used to process nodes level by level in order.

How do we change the direction of traversal in Zigzag Level Order Traversal?

A By using recursion only

B By sorting nodes at each level

C By ignoring alternate levels

D By using a boolean flag to alternate direction each level

A boolean flag helps switch between left-to-right and right-to-left traversal at each level.

What is the output order of nodes at the second level in Zigzag Level Order Traversal?

A Right to left

B Left to right

C Random order

D Same as first level

The second level is traversed in the opposite direction of the first, so right to left.

What is the time complexity of Zigzag Level Order Traversal?

A O(n^2)

B O(log n)

C O(n)

D O(1)

Each node is visited once, so the time complexity is linear, O(n).

Which of these is NOT needed for Zigzag Level Order Traversal?

A Sorting algorithm

B Boolean flag

C Queue

D List to store results

Sorting is not required; direction is controlled by a flag and order of insertion.

Explain how Zigzag Level Order Traversal works step-by-step on a binary tree.

Think about visiting nodes level by level and switching direction.

Describe the data structures and variables needed to implement Zigzag Level Order Traversal.

Focus on what helps track nodes and direction.