Problem Description

Given the root of a binary tree, return the length of the diameter of the tree.

The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

The length of a path between two nodes is represented by the number of edges between them.

Examples

Example 1:

Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3].

Example 2:

Input: root = [1,2]
Output: 1

Constraints:

• The number of nodes in the tree is in the range [1,$10^4$].
• 100 <= Node.val <= 100

解析

定義二元樹的 diameter 為樹內兩點距離最遠的點所形成的距離

給定一個二元樹，希望能夠找出這顆樹的Diameter

首先看下圖

每個結點 node 的 diameter 有兩種可能