DiameterOfBinaryTree.js

// Source : https://leetcode.com/problems/diameter-of-binary-tree
// Author : Dean Shi
// Date   : 2017-03-30

/***************************************************************************************
 *
 * Given a binary tree, you need to compute 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.
 *
 * Example:
 * Given a binary tree
 *
 *           1
 *          / \
 *         2   3
 *        / \
 *       4   5
 *
 * Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].
 *
 * Note:
 * The length of path between two nodes is represented by the number of edges between
 * them.
 *
 *
 ***************************************************************************************/

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var diameterOfBinaryTree = function(root) {
    let max = 0

    maxDepth(root)
    return max

    function maxDepth(root) {
        if (!root) return 0

        const left = maxDepth(root.left)
        const right = maxDepth(root.right)
        max = Math.max(max, left + right)
        return Math.max(left, right) + 1
    }
};