Binary Tree Level Order Traversal

medium

Given the root of a binary tree, return the level order traversal of its nodes' values (i.e., from left to right, level by level).

Test Cases

Copy an input into the main harness and Run to verify

Input

root = [3,9,20,null,null,15,7]

Expected Output

[[3],[9,20],[15,7]]

Input

root = [1]

Expected Output

[[1]]

Input

root = []

Expected Output

[]

Hint 1 — click to reveal

BFS with a queue.

Hint 2 — click to reveal

Snapshot the queue size at each level to group nodes correctly.

Java Compiler