Node Depths

Node Depths

The distance between a node in a Binary Tree and the tree's root is called the node's depth.

Write a function that takes in a Binary Tree and returns the sum of its nodes' depths.

Each BinaryTree node has an integer value, a left child node, and a right child node. Children nodes can either be BinaryTree nodes themselves or None / null.

Sample Input

tree =    1
       /     \
      2       3
    /   \   /   \
   4     5 6     7
 /   \
8     9

Sample Output

16
// The depth of the node with value 2 is 1.
// The depth of the node with value 3 is 1.
// The depth of the node with value 4 is 2.
// The depth of the node with value 5 is 2.
// Etc..
// Summing all of these depths yields 16.

Solution 1

// O(n) time | O(h) space
function nodeDepths(root) {
  let sumOfDepths = 0;
  const stack = [{node: root, depth: 0}];
  while (stack.length > 0) {
    const {node, depth} = stack.pop();
    if (node === null) continue;
    sumOfDepths += depth;
    stack.push({node: node.left, depth: depth + 1});
    stack.push({node: node.right, depth: depth + 1});
  }
  return sumOfDepths
}

// This is the class of the input binary tree.
class BinaryTree {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

// Do not edit the line below.
exports.nodeDepths = nodeDepths;

Solution 2