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binary-tree-level-order-traversal-ii.py
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binary-tree-level-order-traversal-ii.py
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# Time: O(n)
# Space: O(n)
#
# Given a binary tree, return the bottom-up level order traversal of its nodes' values.
# (ie, from left to right, level by level from leaf to root).
#
# For example:
# Given binary tree {3,9,20,#,#,15,7},
# 3
# / \
# 9 20
# / \
# 15 7
# return its bottom-up level order traversal as:
# [
# [15,7],
# [9,20],
# [3]
# ]
#
# Definition for a binary tree node
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None
class Solution:
# @param root, a tree node
# @return a list of lists of integers
def levelOrderBottom(self, root):
if root is None:
return []
result, current = [], [root]
while current:
next_level, vals = [], []
for node in current:
vals.append(node.val)
if node.left:
next_level.append(node.left)
if node.right:
next_level.append(node.right)
current = next_level
result.insert(0, vals)
return result
if __name__ == "__main__":
root = TreeNode(3)
root.left = TreeNode(9)
root.right = TreeNode(20)
root.right.left = TreeNode(15)
root.right.right = TreeNode(7)
result = Solution().levelOrderBottom(root)
print result