JS Basic Binary Tree exercise

binary-tree.js

/**
 * Binary Tree Exercise
 *
 * Given a binary tree, similar to shape as below, write an algorithm
 * to count the number of times each `value` appears.
 *
 * Assumptions:
 *
 * 1. each node will have a `value` prop
 * 2. each node may or may not have a `left` prop
 * 3. each node may or may not have a `right` prop
 *
 * Expected output for the given tree:
 *
 * { tacos: 3, salad: 2, pizza: 2 }
 */

const tree = {
  left: {
    right: {
      value: 'tacos'
    },
    value: 'salad'
  },
  right: {
    left: {
      left: {
        right: {
          value: 'pizza'
        },
        value: 'salad'
      },
      value: 'tacos'
    },
    value: 'pizza'
  },
  value: 'tacos'
}

function countTree(node, accumulator = {}) {
  let obj = Object.keys(accumulator).length ? accumulator : {}

  if (node.left) {
    obj = countTree(node.left, obj)
  }
  if (node.right) {
    obj = countTree(node.right, obj)
  }

  if (node.value) {
    obj[node.value] = obj[node.value] ? obj[node.value] + 1 : 1
  }

  return obj
}

console.log(countTree(tree)) // { tacos: 3, salad: 2, pizza: 2 }