Leetcode #144 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]

.
Difficulty: Medium
学习到了Python 的global变量是怎么用的，CE了好多次，，

# 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 pT(self, root):
if(root is None):
return
ans.append(root.val)
self.pT(root.left)
self.pT(root.right)
return

def preorderTraversal(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
global ans
ans = []
self.pT(root)
return ans