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:
# 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]]
"""
from collections import deque
res = []
if root is None:
return res
is_even = False
my_deque = deque()
my_deque.append(root)
while my_deque:
size = len(my_deque)
lst = []
for _ in range(size):
if is_even:
cur = my_deque.pop()
if cur.right:
my_deque.appendleft(cur.right)
if cur.left:
my_deque.appendleft(cur.left)
else:
cur = my_deque.popleft()
if cur.left:
my_deque.append(cur.left)
if cur.right:
my_deque.append(cur.right)
lst.append(cur.val)
res.append(lst)
is_even = not is_even
return res