Problem 11/30 of LeetCode 30-day challenge

diameterOfBinaryTree.js

/**
 * 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) {
  if(root === null){
    return 0;
  }  
  
  // recursive helper func to help count
  function hasChildren(node) {
      if(node === null) {
        return 0;
      }
      let leftChildren = hasChildren(node.left);
      let rightChildren = hasChildren(node.right);

      return leftChildren > rightChildren ?  leftChildren + 1 : rightChildren + 1;
    }
  // should add from 2 recursive paths -- from the root, then from its children
  let rootDiameter = hasChildren(root.left) + hasChildren(root.right);
  let diameterOfChildren = Math.max(diameterOfBinaryTree(root.left), diameterOfBinaryTree(root.right));
  
  return rootDiameter > diameterOfChildren ? rootDiameter : diameterOfChildren;
};