94. Binary Tree Inorder Traversal

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
# 递归，中序遍历方法
class Solution(object):
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        res = []
        self.helper(root, res)
        return res
    
    def helper(self, root, res):
        if root:
            self.helper(root.left, res)
            res.append(root.val)
            self.helper(root.right, res)

#非递归方法
class Solution(object):
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        res = []
        stack = []
        while True:
            while root:
                stack.append(root)
                root = root.left
            if not stack:
                return res
            node = stack.pop()
            res.append(node.val)
            root = node.right
        
        return res

def inorderTraversal(self, root):        """        :type root: TreeNode        :rtype: List[int]        """        res = []        stack = []        while True:            while root:                stack.append(root)                root = root.left            if not stack:                return res            node = stack.pop()            res.append(node.val)            root = node.right                return res