leetcode-二叉树的中序遍历

94. 二叉树的中序遍历

此题可以使用递归方法：

1.确定递归函数的参数和返回值

2.确定终止条件

3.确定单层递归的逻辑

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def inorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        res = []
        def helper(root, res):
            if root:
                helper(root.left, res)
                res.append(root.val)
                helper(root.right, res)
        helper(root, res)
        return res

使用迭代法

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def inorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        res = []
        stack = []
        cur = root
        while cur or stack:
            while cur:
                stack.append(cur)
                cur = cur.left
            cur = stack.pop()
            res.append(cur.val)
            cur = cur.right
        return res