Invert a Binary Tree using GoLang

This problem was inspired by this original tweet by Max Howell:
Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.

Invert a binary tree.
Example:

Input:
     4
   /   \
  2     7
 / \   / \
1   3 6   9
Output:
     4
   /   \
  7     2
 / \   / \
9   6 3   1

GoLang Implementation of Inverting a Binary Tree

Inverting Binary Tree can be done efficiently using Recursion. We recursively invert the left and right trees and then swap them. We can also swap and then invert – which will work as well.

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func invertTree(root *TreeNode) *TreeNode {
    if root == nil {
        return nil
    }
    var left = invertTree(root.Left)
    var right = invertTree(root.Right)
    root.Left = right
    root.Right = left
    return root
}

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func invertTree(root *TreeNode) *TreeNode {
    if root == nil {
        return nil
    }
    var left = invertTree(root.Left)
    var right = invertTree(root.Right)
    root.Left = right
    root.Right = left
    return root
}

GoLang supports the Tuple assignment meaning that we can write this a bit cleaner/shorter.

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func invertTree(root *TreeNode) *TreeNode {
    if root != nil {
        root.Left, root.Right = invertTree(root.Right), invertTree(root.Left)
    }
    return root
}

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func invertTree(root *TreeNode) *TreeNode {
    if root != nil {
        root.Left, root.Right = invertTree(root.Right), invertTree(root.Left)
    }
    return root
}

See also other posts on inverting the binary tree:

–EOF (The Ultimate Computing & Technology Blog) —

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GoLang Implementation of Inverting a Binary Tree

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GoLang Implementation of Inverting a Binary Tree

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