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Decode the Coding Interview in Go: Real-World Examples

Binary Tree Zigzag Level Order Traversal

Explore how to implement zigzag level order traversal of binary trees using a breadth-first search approach with a deque. Understand the alternating pattern between left-to-right and right-to-left traversal and learn to apply this technique efficiently, including analyzing time and space complexities.

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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 element in each level in a two-dimensional array.

Let’s look at an example:

Coding exercise

Go (1.6.2)
package main
import (
  "fmt"
  "strconv"
  "encoding/json"
)
type TreeNode struct{
    val int
    left *TreeNode
    right *TreeNode
}
func zigzagLevelOrder(root *TreeNode) [][]int {
    // write your code here
    return [][]int{}
}
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 ...