94. 二叉树的中序遍历

题目

给定一个二叉树的根节点 root ,返回它的 中序 遍历。

示例 1:

输入:root = [1,null,2,3]
输出:[1,3,2]

示例 2:

输入:root = []
输出:[]

示例 3:

输入:root = [1]
输出:[1]

示例 4:

输入:root = [1,2]
输出:[2,1]

示例 5:

输入:root = [1,null,2]
输出:[1,2]

提示:

  • 树中节点数目在范围 [0, 100] 内
  • -100 <= Node.val <= 100

进阶: 递归算法很简单,你可以通过迭代算法完成吗?

代码

# 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: TreeNode) -> List[int]:
        res = []
        if root is not None:
            stack = []
            while stack or root is not None:
                if root is not None:
                    stack.append(root)
                    root = root.left
                else:
                    root = stack.pop()
                    res.append(root.val)
                    root = root.right
        return res
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