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BinaryTreeLevelOrderTraversalII.py
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BinaryTreeLevelOrderTraversalII.py
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from collections import deque
from typing import List
# Definition for a binary tree node.
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None
class Solution:
def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:
if not root:
return []
result = []
q = deque()
q.append(root)
while q:
level = []
for _ in range(len(q)):
node = q.popleft()
level.append(node.val)
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
result.append(level)
result.reverse()
return result
########
# Test #
########
# 3
# / \
# 9 20
# / \
# 15 7
root = TreeNode(3)
node1 = TreeNode(9)
node2 = TreeNode(20)
node3 = TreeNode(15)
node4 = TreeNode(7)
root.left = node1
root.right = node2
node2.left = node3
node2.right = node4
result = Solution().levelOrderBottom(root)
print(result)
# expected: [[15, 7], [9, 20], [3]]