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Solve Tree View and Triplet Sum | Meta Coding Question

Quick Overview

This multipart question evaluates proficiency with tree-based data structures and array-based algorithmic problem solving, focusing on reasoning about which nodes are visible from a binary tree's right side and identifying unique zero-sum triplets in an integer array; it tests concepts such as tree traversal, duplicate handling, and algorithmic complexity analysis. These problems are commonly asked to assess algorithmic problem-solving ability, manipulation of fundamental data structures, and attention to edge cases and performance, and they fall under the Coding & Algorithms category with a focus on practical application of algorithmic concepts supported by conceptual understanding of data structures and complexity.

Solve Tree View and Triplet Sum

Company: Meta

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: easy

Interview Round: Technical Screen

You are asked to solve two coding problems. **Problem 1: Return the nodes visible from the right** Given the root of a binary tree, return the values of the nodes that would be visible if the tree were viewed from its right side. Return the values from top to bottom. Example: ```text Input: 1 / \ 2 3 \ \ 5 4 Output: [1, 3, 4] ``` Constraints: - The number of nodes is in the range `[0, 10^4]`. - Node values are integers. **Problem 2: Find unique triplets with zero sum** Given an integer array `nums`, return all unique triplets `[a, b, c]` such that `a + b + c = 0`. The solution set must not contain duplicate triplets. The order of triplets and the order of numbers inside each triplet do not matter. Example: ```text Input: nums = [-1, 0, 1, 2, -1, -4] Output: [[-1, -1, 2], [-1, 0, 1]] ``` Constraints: - `3 <= nums.length <= 3000` - `-10^5 <= nums[i] <= 10^5`

Quick Answer: This multipart question evaluates proficiency with tree-based data structures and array-based algorithmic problem solving, focusing on reasoning about which nodes are visible from a binary tree's right side and identifying unique zero-sum triplets in an integer array; it tests concepts such as tree traversal, duplicate handling, and algorithmic complexity analysis. These problems are commonly asked to assess algorithmic problem-solving ability, manipulation of fundamental data structures, and attention to edge cases and performance, and they fall under the Coding & Algorithms category with a focus on practical application of algorithmic concepts supported by conceptual understanding of data structures and complexity.

Part 1: Right Side View of a Binary Tree

You are given a binary tree serialized as a Python list in level-order, where `None` represents a missing child. Return the values of the nodes visible when the tree is viewed from the right side, from top to bottom.

Constraints

The number of nodes is in the range [0, 10^4].
Node values are integers.
The input list is a valid level-order serialization of a binary tree.
`None` indicates that a child is missing.

Examples

Input: [1, 2, 3, None, 5, None, 4]

Expected Output: [1, 3, 4]

Explanation: From the right, you see 1 at level 0, 3 at level 1, and 4 at level 2.

Input: [1, 2, 3, 4, None, None, None]

Expected Output: [1, 3, 4]

Explanation: Although 4 is on the left subtree, it is still the only visible node at its depth from the right.

Input: []

Expected Output: []

Explanation: An empty tree has no visible nodes.

Input: [7]

Expected Output: [7]

Explanation: A single-node tree is visible from every side.

Hints

A level-order traversal lets you process one depth level at a time.
At each level, the last node you visit is the one visible from the right.

Part 2: Find Unique Triplets With Zero Sum

Given an integer array `nums`, return all unique triplets `[a, b, c]` such that `a + b + c = 0`. The result must not contain duplicate triplets. For deterministic grading, return each triplet in nondecreasing order, and return the full list of triplets in lexicographic order.

Constraints

3 <= nums.length <= 3000
-10^5 <= nums[i] <= 10^5
The solution set must not contain duplicate triplets.

Examples

Input: [-1, 0, 1, 2, -1, -4]

Expected Output: [[-1, -1, 2], [-1, 0, 1]]

Explanation: These are the only two unique triplets whose sum is zero.

Input: [0, 0, 0, 0]

Expected Output: [[0, 0, 0]]

Explanation: Even though there are many ways to pick three zeros, the triplet should appear only once.

Input: [1, 2, -2, -1]

Expected Output: []

Explanation: No three numbers add up to zero.

Input: [-2, 0, 1, 1, 2]

Expected Output: [[-2, 0, 2], [-2, 1, 1]]

Explanation: There are exactly two unique zero-sum triplets.

Hints

Sorting the array turns the problem into finding pairs with a target for each fixed first number.
After finding a valid triplet, move both pointers and skip repeated values to avoid duplicates.

Last updated: May 19, 2026

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Quick Overview

Solve Tree View and Triplet Sum

Company: Meta

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: easy

Interview Round: Technical Screen

Part 1: Right Side View of a Binary Tree

Constraints

The number of nodes is in the range [0, 10^4].
Node values are integers.
The input list is a valid level-order serialization of a binary tree.
`None` indicates that a child is missing.

Examples

Input: [1, 2, 3, None, 5, None, 4]

Expected Output: [1, 3, 4]

Explanation: From the right, you see 1 at level 0, 3 at level 1, and 4 at level 2.

Input: [1, 2, 3, 4, None, None, None]

Expected Output: [1, 3, 4]

Explanation: Although 4 is on the left subtree, it is still the only visible node at its depth from the right.

Input: []

Expected Output: []

Explanation: An empty tree has no visible nodes.

Input: [7]

Expected Output: [7]

Explanation: A single-node tree is visible from every side.

Hints

A level-order traversal lets you process one depth level at a time.
At each level, the last node you visit is the one visible from the right.

Part 2: Find Unique Triplets With Zero Sum

Constraints

3 <= nums.length <= 3000
-10^5 <= nums[i] <= 10^5
The solution set must not contain duplicate triplets.

Examples

Input: [-1, 0, 1, 2, -1, -4]

Expected Output: [[-1, -1, 2], [-1, 0, 1]]

Explanation: These are the only two unique triplets whose sum is zero.

Input: [0, 0, 0, 0]

Expected Output: [[0, 0, 0]]

Explanation: Even though there are many ways to pick three zeros, the triplet should appear only once.

Input: [1, 2, -2, -1]

Expected Output: []

Explanation: No three numbers add up to zero.

Input: [-2, 0, 1, 1, 2]

Expected Output: [[-2, 0, 2], [-2, 1, 1]]

Explanation: There are exactly two unique zero-sum triplets.

Hints

Sorting the array turns the problem into finding pairs with a target for each fixed first number.
After finding a valid triplet, move both pointers and skip repeated values to avoid duplicates.

Last updated: May 19, 2026

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