Binary Tree Level Order Traversal


Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).
For example:
Given binary tree {3,9,20,#,#,15,7},
    3
   / \
  9  20
    /  \
   15   7
return its level order traversal as:
[
  [3],
  [9,20],
  [15,7]
]
Solution: BFS. The following code passes LeetCode Large OJ.

For Binary Tree Level Order Traversal II, either reverse, or insert in the beginning.

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