What is the brute force approach and complexity for Find Largest Value in Each Tree Row?

Store each full row in a list, then take the largest value in each list with time complexity O(N) and space complexity O(N).

What is the optimal approach and complexity for Find Largest Value in Each Tree Row?

Level-order traversal; keep a running max for each round and write it out when the round ends with optimal time complexity O(N) and space complexity O(W).

How do you identify the pattern for Find Largest Value in Each Tree Row?

Look for key signals in the prompt: "largest value in each row" indicates One maximum per row. It is a per-level aggregate, like the averages question, with max in place of sum.; "row (0-indexed)" indicates A row is a depth, so the answer is indexed by depth and each row gets exactly one value.; "return an array" indicates The answer is ordered top to bottom, which is the order in which BFS finishes the rows..

Find Largest Value in Each Tree Row

Medium·LeetCode #515 Pro OnlySlight Variation

LeetCode

Problem Statement

You are given the root of a binary tree.

A row is all the nodes at the same depth. Row 0 is the root's row, row 1 is the row below it, and so on.

For each row, find the largest node value in that row. Return one number per row, from the top row down.

Input

The root of a binary tree. The tree may be empty.

Output

An array with one number per row: the largest value in that row, top to bottom.

Example 1

Input: root = [1, 3, 2, 5, 3, null, 9]

Output: [1, 3, 9]

Row 0 has only 1. Row 1 has 3 and 2, so the largest is 3. Row 2 has 5, 3 and 9, so the largest is 9.

Example 2

Input: root = [1, 2, 3]

Output: [1, 3]

Row 0 has 1. Row 1 has 2 and 3, so the largest is 3.

Constraints

• The number of nodes is between 0 and 10^4.
• −2^31 ≤ Node.val ≤ 2^31 − 1

Pattern Recognition Clues

Recognising these key signals in the problem description immediately identifies the pattern:

“largest value in each row”

→ One maximum per row. It is a per-level aggregate, like the averages question, with max in place of sum.

“row (0-indexed)”

→ A row is a depth, so the answer is indexed by depth and each row gets exactly one value.

“return an array”

→ The answer is ordered top to bottom, which is the order in which BFS finishes the rows.

Approach Complexity Ladder

Brute Force — store each row, then take the maxO(N)O(N)

Store each full row in a list, then take the largest value in each list

Optimal — BFS, running max per roundO(N)O(W)

Level-order traversal; keep a running max for each round and write it out when the round ends

Brute Force Intuition

Run a level-order traversal and save each row as a complete list. When the traversal ends, the answer is the largest value in each list.

Recognition rule for this sub-pattern:

Compute something per level: last node (right view), max, average, width.

Remember this · Tree BFS

Trigger

Level order, per-level max/average, right side view, minimum depth, nodes at distance k.

Think

Does the question care about depth / rows rather than paths?

Key question

How many nodes are in the current level (queue size at the start of the level)?

Brute2Best Pro Content

Unlock Complete Visual Walkthrough & Optimal C++

The interactive animated dry-run player, optimized C++ implementation, state invariant derivations, and edge-case breakdown for this question are part of Brute2Best Pro. The anchor question of every sub-pattern is completely free.

All 440 visual dry runs & algorithms

Interactive step-by-step playback with pointer & array state transitions

52 comprehensive LLD chapters

Interactive UML diagrams, real-world stories (Food Delivery, Trading, RPG), and practice solutions

40 C++ basics labs & hardware memory models

Vtables, byte layouts, assembly insights, and multi-threading race conditions

Production-ready C++23 source code

Modern idioms, clean contracts, time/space complexity derivations, and interview takeaways

Create Free Account Log in

First anchor question per pattern, Part 1 LLD & Module 1 C++ basics are 100% Free forever.

Beyond The LeetCode Problem

How this concept connects to System Design & C++ Systems

Bridge DSA with production engineering

Top engineering interviews test whether you understand how algorithms like Tree BFS translate into production architectures and low-level memory mechanics.

LLD Architecture