#0237

Binary Tree Inorder Traversal

EasyDSA18 min10 XP

Problem

A tree node is represented as [value, left, right], and an empty child is None. Return the inorder traversal values: left, root, right.

Why This Matters

Tree traversal is the foundation for BST checks, tree DP, recursion, and graph thinking.

Function Signature

def inorder(root):

Examples

Example 1

Inputroot = [2, [1, None, None], [3, None, None]]

Output[1, 2, 3]

Visit left subtree, then root value, then right subtree.

Constraints

Return the exact requested value.
Handle empty or small inputs when the prompt allows them.
Prefer the target DSA pattern over brute force when the input can grow.

CodePython

def inorder(root):
    """
    Input example: root = [2, [1, None, None], [3, None, None]]
    Return: [1, 2, 3]
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return []

def inorder(root):
    """
    Input example: root = [2, [1, None, None], [3, None, None]]
    Return: [1, 2, 3]
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return []

Visible browser tests run here when available.

Testcases2 visible / 3 hidden categories

Balanced three nodes

Input[2, [1, None, None], [3, None, None]]

Expected[1, 2, 3]

Left-root-right gives sorted values for this BST.

Right leaning

Input[1, None, [2, None, [3, None, None]]]

Expected[1, 2, 3]

Empty left children are skipped.

Hidden Test Categories

empty treesingle nodeunbalanced tree