LEETCODE —— Binary Tree的3 题 —— 3种非Recursive遍历

Binary Tree Preorder Traversal

Given a binary tree, return the preorder traversal of its nodes' values.

For example:
Given binary tree

{1,#,2,3}

,

1
\
2
/
3

return

[1,2,3]

.

Note: Recursive solution is trivial, could you do it iteratively?

'''
Created on Nov 19, 2014

@author: ScottGu<gu.kai.66@gmail.com, 150316990@qq.com>
'''
# 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 integers
def postorderTraversal(self, root):
visited={}
stack=[]
vals=[]
if(root==None): return vals
node=root

stack.append(node)
visited[node]=1

while(len(stack)!=0):
node=stack[-1]
if(node.left !=None and visited.has_key(node.left)==False):
stack.append(node.left)
visited[node.left]=1
continue
else:
if(node.right!=None and visited.has_key(node.right)==False):
stack.append(node.right)
visited[node.right]=1
continue
node=stack.pop()
if(node==None): continue
vals.append(node.val)

return vals

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