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Decode the Coding Interview in Scala: Real-World Examples

Flip Equivalent Binary Trees

Understand how to verify whether two binary trees are flip equivalent by learning the recursive method to swap and compare child subtrees. This lesson guides you through base cases, recursive checks, and complexity considerations to implement an effective flip equivalency function.

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Description

Let’s start by defining what a flip operation for a binary tree is. We can define it as:

“Choosing any node and swapping the right and left child subtrees.”

A binary tree, T, is flip equivalent to another binary tree, S, if we can make T equal to S after some number of flip operations.

Given the roots of two binary trees, root1 and root2, you have to find out whether the trees are flip equivalent to each other or not. The flipEquiv function should return True if the binary trees are equivalent. Otherwise, it will return False.

Example

Let’s look at the example below:

Coding exercise

Scala
class TreeNode(var value:Int=0, var left:TreeNode=null, var right:TreeNode=null) {
}
object Solution {
  def flipEquiv(root1: TreeNode, root2: TreeNode): Boolean = {
    // write your code here
    false
  }
}
Flip equivalent binary tree

Solution

We implement the flipEquiv function using recursion. Like any recursive function, we start by defining the base conditions. We have two base conditions:

  1. If root1 or root2 is null, they are equivalent if and only if they are both null.

  2. If root1 and root2 have different values, they aren’t ...