level_order.py

"""
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,null,null,15,7],
 3
 / \
 9 20
 / \
 15 7
return its level order traversal as:
[
 [3],
 [9,20],
 [15,7]
]
"""


deflevel_order(root):
ans= []
ifnotroot:
returnans
level= [root]
whilelevel:
current= []
new_level= []
fornodeinlevel:
current.append(node.val)
ifnode.left:
new_level.append(node.left)
ifnode.right:
new_level.append(node.right)
level=new_level
ans.append(current)
returnans