Decode the Coding Interview in Java: Real-World Examples/

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Binary Tree Zigzag Level Order Traversal

Binary Tree Zigzag Level Order Traversal

Understand and solve the interview question "Binary Tree Zigzag Level Order Traversal".

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Description

Given a binary tree T, you have to find its nodes’ zigzag level order traversal. The zigzag level order traversal corresponds to traversing nodes from left to right and then right to left for the next level, alternating between.

You have to return the elements in each level in a two-dimensional array.

Let’s look at an example:

Coding exercise

main.java
TreeNode.java
class Solution {
    public static List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        // write your code here
        return new ArrayList<List<Integer>>();
    }
}
Binary Tree Zigzag Level Order Traversal

Solution

As per the problem statement, we need to traverse the tree in a level-by-level zigzag order. An intuitive approach for this problem would be to use Breadth-First Search (BFS). By default, BFS provides ordering from left to right within a single level.

We will need to modify BFS a little to get our desired output, a zigzagzigzag ...