Diameter of Binary Tree

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.

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, 104].
• -100 <= Node.val <= 100

Solution (JavaScript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var diameterOfBinaryTree = function(root) {
    let diameter = 0;
    const depth = (node) => {
        if(!node) {
            return 0;
        }
        let leftDepth = 0, rightDepth = 0;
        if (node.left) leftDepth = 1+depth(node.left);
        if (node.right) rightDepth = 1+depth(node.right);
        if (leftDepth + rightDepth > diameter) diameter = leftDepth + rightDepth;
        return Math.max(leftDepth, rightDepth);
    }
    depth(root);
    return diameter;
};