[Leet Code] Binary Tree Level Order Traversal II

3
/ \
9 20
/ \
15 7
[
[15,7],
[9,20],
[3]
]
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution(object):
def levelOrderBottom(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""
if root:
elements = [[root.val]]
stack = [root]
self.helper(root, stack, elements)
return reversed(elements)
return root
def helper(self, root, stack, elements):
while len(stack) > 0:
values = []
length = len(stack)
for i in range(length):
node = stack.pop(0)
if node.left:
stack.append(node.left)
values.append(node.left.val)
if node.right:
stack.append(node.right)
values.append(node.right.val)
if values != []:
elements.append(values)

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Matthew Boyd

Matthew Boyd

Learning, and posting my findings!