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]
]
Python Solution
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def zigzagLevelOrder(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""
if not root: return []
res = []
l = [root]
odd = 0
while l:
r = []
vals = []
for node in l:
vals.append(node.val)
if node.left: r.append(node.left)
if node.right: r.append(node.right)
if odd: vals.reverse()
res.append(vals)
odd ^= 1
l = r
return res
Summary:
- nothing to say
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