94. Binary Tree Inorder Traversal

[1,null,2,3]

1
\
2
/
3

[1,3,2]

class Solution(object):
def inorderTraversal(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root:
return []
return self.inorderTraversal(root.left) + [root.val] + self.inorderTraversal(root.right)

class Solution(object):
def inorderTraversal(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root:
return []
stack = []
node = root
result = []　　　
while node or len(stack) > 0:
while node:
stack.append(node)
node = node.left
node = stack.pop()
result.append(node.val)
node = node.right
return result