#0277

Diameter of Binary Tree

MediumDSA28 min20 XP

Problem

A tree node is [value, left, right]. Return the diameter measured in edges.

Why This Matters

Diameter is the first tree problem where the answer may pass through a node while the return value is only one side depth.

Function Signature

def diameter(root):

Examples

Example 1

Inputroot = [1,[2,[4,None,None],[5,None,None]],[3,None,None]]

Output3

The longest path is 4 -> 2 -> 1 -> 3, which has 3 edges.

Constraints

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

CodePython

def diameter(root):
    """
    Input example: root = [1,[2,[4,None,None],[5,None,None]],[3,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 diameter(root):
    """
    Input example: root = [1,[2,[4,None,None],[5,None,None]],[3,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

Diameter through root

Inputclassic five-node tree

Expected3

Left depth 2 and right depth 1 combine at the root.

Single node

Input[1]

Expected0

One node has no edge path.

Hidden Test Categories

empty treediameter entirely inside one subtreelong chain