# 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 preorderTraversal(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
s = [] # use as a stack
res = [] # stores result
if (root == None):
return res
else:
s.append(root)
while(s):
# if s is empty, s is False. not s is True
curr = s.pop()
res.append(s.val)
s.append(s.right) # pre-order print left first, so push right first
s.append(s.left)
return res
可以优化。见下一个帖子。
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