<filename>problems/tree/Solution103.py<gh_stars>0
"""   
   Tree
   
   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).
   
   For example: Given binary tree [3,9,20,null,null,15,7], 
   
         3 
        / \ 
       9  20 
      / \ 
     15  7
   return its zigzag level order traversal as: 
   [ 
   [3], 
   [20,9], 
   [15,7] 
   ]
   
   IDEA: be aware of the even or odd the current level is and push into list from tail or head
"""

class Solution103:
    pass
