ZigZag Level Order Traversal BT

Given a binary tree, return the zigzag level order traversal of its nodes’ values. (ie, from left to right, then right to left for the next level and alternate between).

Example :
Given binary tree

    3
   / \
  9  20
    /  \
   15   7

return

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

NOTE: You only need to implement the given function. Do not read input, instead use the arguments to the function. Do not print the output, instead return values as specified. Still have a question? Checkout Sample Codes for more details.