#107

Binary Tree Level Order Traversal II

medium · verified · 67.7% accepted · 5,155 likes · top 74%

tree · breadth-first search · binary tree

⊣ practice⊣ quiz⊣ open on leetcode ↗

Description

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

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: [[15,7],[9,20],[3]]

Example 2:

Input: root = [1]
Output: [[1]]

Example 3:

Input: root = []
Output: []

Solution