#0275

Maximum Depth of Binary Tree

EasyDSA18 min10 XP

Problem

A tree node is [value, left, right], and an empty child is None. Return the maximum depth of the tree.

Why This Matters

Tree depth is the simplest recursive tree problem and the base for balance, diameter, and path questions.

Function Signature

def max_depth(root):

Examples

Example 1

Inputroot = [3, [9, None, None], [20, [15, None, None], [7, None, None]]]

Output3

The longest path is 3 -> 20 -> 15 or 3 -> 20 -> 7.

Constraints

Return the exact requested value.
Handle edge cases cleanly.
Use the intended DSA pattern when brute force would scale poorly.

CodePython

def max_depth(root):
    """
    Input example: root = [3, [9, None, None], [20, [15, None, None], [7, None, None]]]
    Return: 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 0

def max_depth(root):
    """
    Input example: root = [3, [9, None, None], [20, [15, None, None], [7, None, None]]]
    Return: 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 0

Visible browser tests run here when available.

Testcases2 visible / 3 hidden categories

Three levels

Inputbalanced-ish tree

Expected3

The deepest leaf is three nodes from the root.

Empty tree

InputNone

Expected0

No nodes means depth zero.

Hidden Test Categories

single nodeleft-heavy treeright-heavy tree