Is Evaluate Boolean Binary Tree easy or hard?

LeetCode classifies Evaluate Boolean Binary Tree as an Easy problem. The challenge mainly tests basic binary tree traversal and recursion. Once you recognize it as an expression tree evaluation, the implementation becomes straightforward.

Evaluate Boolean Binary Tree Python/Java solution

In Python or Java, implement a recursive function that returns the boolean value of a subtree. If the node is a leaf, return true for value 1 and false for value 0. Otherwise recursively evaluate the left and right children and apply OR (2) or AND (3) depending on the node value.

How to solve Evaluate Boolean Binary Tree in O(n)?

Use a Depth-First Search traversal. Recursively evaluate the left and right children of each internal node, then apply the operator stored at the node: OR for value 2 and AND for value 3. Since every node is processed once and each operation is constant time, the overall complexity remains O(n).

What is the best approach for Evaluate Boolean Binary Tree?

The recursive Depth-First Search approach is the most efficient and straightforward method. Traverse the binary tree, evaluate leaf nodes directly, and combine results using OR (2) or AND (3) operations at internal nodes. This processes each node once, resulting in O(n) time complexity and O(h) recursion stack space.

Is Evaluate Boolean Binary Tree asked at Google/Amazon/Meta?

Expression tree evaluation and DFS-based tree problems frequently appear in interviews at companies like Google, Amazon, and Meta. Variations of boolean expression trees and binary tree evaluation are commonly used to test recursion and tree traversal skills.

What data structure is used in Evaluate Boolean Binary Tree?

The core data structure is a binary tree where nodes represent either boolean values or logical operators. The algorithm typically uses Depth-First Search with recursion or an explicit stack to traverse and evaluate the tree.

What is the time complexity of Evaluate Boolean Binary Tree?

The time complexity is O(n) because each node in the binary tree is visited exactly once during the traversal. The space complexity is O(h), where h is the height of the tree, due to the recursion stack or explicit stack used during DFS.

Description Hints 2 Solution Video 14:55

2331. Evaluate Boolean Binary Tree

Easy82.7% acceptance1 company

You are given the root of a full binary tree with the following properties:

Leaf nodes have either the value 0 or 1, where 0 represents False and 1 represents True.
Non-leaf nodes have either the value 2 or 3, where 2 represents the boolean OR and 3 represents the boolean AND.

The evaluation of a node is as follows:

If the node is a leaf node, the evaluation is the value of the node, i.e. True or False.
Otherwise, evaluate the node's two children and apply the boolean operation of its value with the children's evaluations.

Return the boolean result of evaluating the root node.

A full binary tree is a binary tree where each node has either 0 or 2 children.

A leaf node is a node that has zero children.

Example 1:

Input: root = [2,1,3,null,null,0,1]
Output: true
Explanation: The above diagram illustrates the evaluation process.
The AND node evaluates to False AND True = False.
The OR node evaluates to True OR False = True.
The root node evaluates to True, so we return true.

Example 2:

Input: root = [0]
Output: false
Explanation: The root node is a leaf node and it evaluates to false, so we return false.

Constraints:

The number of nodes in the tree is in the range [1, 1000].
0 <= Node.val <= 3
Every node has either 0 or 2 children.
Leaf nodes have a value of 0 or 1.
Non-leaf nodes have a value of 2 or 3.

Asked at 1 company

Google

Topics

Hints open one at a time

Hint 1

Traverse the tree using depth-first search in post-order.

Hint 2

Can you use recursion to solve this easily?

14:55

Still stuck?Read 3 approaches, or watch a walkthrough.

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