#2265 - Count Nodes Equal to Average of Subtree

Medium • View on LeetCode • View on GitHub

Problem Description

Given the root of a binary tree, return the number of nodes where the value of the node is equal to the average of the values in its subtree.

Note:

The average of n elements is the sum of the n elements divided by n and rounded down to the nearest integer.
A subtree of root is a tree consisting of root and all of its descendants.

Solution

/**
 * 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 averageOfSubtree = function(root) {
  let count = 0;
  traverse(root);
  return count;

  function traverse(node) {
    if (!node) return [0, 0];

    const [leftSum, leftCount] = traverse(node.left);
    const [rightSum, rightCount] = traverse(node.right);
    const totalSum = leftSum + rightSum + node.val;
    const totalCount = leftCount + rightCount + 1;

    if (Math.floor(totalSum / totalCount) === node.val) {
      count++;
    }

    return [totalSum, totalCount];
  }
};