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pseudo-palindromic-paths-in-a-binary-tree.py
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pseudo-palindromic-paths-in-a-binary-tree.py
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# Time: O(n)
# Space: O(h)
# 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 pseudoPalindromicPaths (self, root):
"""
:type root: TreeNode
:rtype: int
"""
result = 0
stk = [(root, 0)]
while stk:
node, count = stk.pop()
if not node:
continue
count ^= 1 << (node.val-1)
result += int(node.left == node.right and count&(count-1) == 0)
stk.append((node.right, count))
stk.append((node.left, count))
return result
# Time: O(n)
# Space: O(h)
class Solution2(object):
def pseudoPalindromicPaths (self, root):
"""
:type root: TreeNode
:rtype: int
"""
def dfs(node, count):
if not root:
return 0
count ^= 1 << (node.val-1)
return int(node.left == node.right and count&(count-1) == 0) + \
dfs(node.left, count) + dfs(node.right, count)
return dfs(root, 0)