Solving Binary Tree Level Order Traversal II in go. Please try yourself first to solve the problem and submit your implementation to LeetCode before looking into solution.

Problem Description

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

For example: Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its bottom-up level order traversal as:

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

See the full details of the problem Binary Tree Level Order Traversal II at LeetCode

Originally posted at: @github.com/halfrost/LeetCode-Go