1120-maximum-average-subtree.js

/**

Given the root of a binary tree, find the maximum average value of any subtree of that tree.
(A subtree of a tree is any node of that tree plus all its descendants.
The average value of a tree is the sum of its values, divided by the number of nodes.)

Example 1:

Input: [5,6,1]
Output: 6.00000
Explanation: 
For the node with value = 5 we have an average of (5 + 6 + 1) / 3 = 4.
For the node with value = 6 we have an average of 6 / 1 = 6.
For the node with value = 1 we have an average of 1 / 1 = 1.
So the answer is 6 which is the maximum.

Note:

The number of nodes in the tree is between 1 and 5000.
Each node will have a value between 0 and 100000.
Answers will be accepted as correct if they are within 10^-5 of the correct answer.

*/

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
const maximumAverageSubtree = function(root) {
  let max = -Number.MIN_VALUE;
  function helper(root) {
    if (!root) return [0, 0]; // [value, number of nodes]
    const [lTotal, lNum] = helper(root.left);
    const [rTotal, rNum] = helper(root.right);
    max = Math.max(max, (rTotal + lTotal + root.val) / (rNum + lNum + 1));
    return [lTotal + rTotal + root.val, lNum + rNum + 1];
  }
  helper(root);
  return max;
};