94. Binary Tree Inorder Traversal

Edited by Charles

Easy · Python · Binary Tree

Problem

Read the original problem on LeetCode.

The official page contains the problem statement, examples, and constraints.

Explanation, examples & other approaches

Core idea

Reference to 144. Binary Tree Preorder Traversal (Preorder, Postorder and Inorder are all listed!)

Original study notes follow, including intermediate snippets and earlier attempts.

Reference to 144. Binary Tree Preorder Traversal (Preorder, Postorder and Inorder are all listed!)

Study record

Field	Value
Attempts	1
Mastery	❚
The Latest Attempt	January 12, 2026

Python solution

# 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]:
        if not root:
            return []

        stack = []
        result = []
        cur = root

        while cur or stack:
            if cur:
                stack.append(cur)
                cur = cur.left
            else:
                cur = stack.pop()
                result.append(cur.val)
                cur = cur.right

        return result

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