Zigzag Level Order Traversal in DSA Go - 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.

intermediate

Why do we use two stacks or a deque in Zigzag Level Order Traversal?

To keep track of nodes in the current level and the next level while controlling the order of traversal direction (left to right or right to left).

intermediate

In Zigzag Level Order Traversal, what determines the order of adding child nodes to the next level?

The current traversal direction. If going left to right, add left child first then right child. If right to left, add right child first then left child.

beginner

What is the time complexity of Zigzag Level Order Traversal?

O(n), where n is the number of nodes in the tree, because each node is visited exactly once.

beginner

Show the output of Zigzag Level Order Traversal for this tree:<br> 1<br> / \<br> 2 3<br> / \ \<br>4 5 6

The output is [[1], [3, 2], [4, 5, 6]].<br>Level 1: left to right → [1]<br>Level 2: right to left → [3, 2]<br>Level 3: left to right → [4, 5, 6]

What data structure is commonly used to implement Zigzag Level Order Traversal?

A Queue or deque

B Stack or deque

C Hash map

D Linked list

Stacks or deques help alternate the order of traversal by controlling the order of node processing.

In Zigzag traversal, if the current level is traversed left to right, how are child nodes added for the next level?

A Right child first, then left child

B Only left child

C Only right child

D Left child first, then right child

When traversing left to right, add left child first to maintain correct order for next level.

What is the output of Zigzag Level Order Traversal for a tree with only one node?

A []

B [[]]

C [[node_value]]

D [node_value]

The output is a list containing one list with the single node's value.

What is the main difference between normal level order traversal and zigzag level order traversal?

A Zigzag alternates direction each level, normal always left to right

B Zigzag uses recursion, normal uses iteration

C Zigzag only visits leaf nodes

D Normal traversal uses stacks, zigzag uses queues

Zigzag traversal changes direction at each level, normal traversal always goes left to right.

What is the space complexity of Zigzag Level Order Traversal?

A O(n)

B O(log n)

C O(1)

D O(n^2)

Space complexity is O(n) because we store nodes of each level in data structures.

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

Think about how you would walk through the tree visiting nodes in a zigzag pattern.

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

Focus on how to keep track of nodes and direction for each level.