https://adventofcode.com/2018/day/8

day8.js

// https://adventofcode.com/2018/day/8
// https://jsfiddle.net/keipixel/fuyhq4az/

const data = '2 3 0 3 10 11 12 1 1 0 1 99 2 1 1 2'
// {
//  meta: [1, 1, 2],
//  children: [
//    {
//      meta: [10, 11, 12],
//      children: []
//    },
//    {
//      meta: [2],
//      children: [
//        {
//          meta: [99],
//          children: []
//        }
//      ]
//    }
//  ]
// }

const treeify = d => {
  const node = {
    meta: [],
    children: []
  }
  const childCount = d.shift()
  const metaCount = d.shift()
  // console.log(`has ${metaCount} meta entries & ${childCount} children`)
  if (childCount) {
    for (let i = 0; i < childCount; i++) {
      node.children.push(treeify(d))
    }
  }
  // all children should be deleted
  node.meta = d.splice(0, metaCount)
  return node
}

const sumMetas = tree => {
  const sum = tree.meta.reduce((sum, i) => sum + 1 * i, 0)
  if (tree.children) {
    return sum + tree.children.map(child => sumMetas(child)).reduce((sum, i) => sum + 1 * i, 0)
  }
  return sum
}

const getRootValue = tree => {
  return tree.meta
    .map(meta => {
      const node = tree.children[meta - 1]
      // console.log(node)
      if (node) {
        if (node.children.length === 0) {
          return node.meta.reduce((sum, i) => sum + 1 * i, 0)
        } else {
          return getRootValue(node)
        }
      }
      return 0
    })
    .reduce((sum, i) => sum + 1 * i, 0)
}

const tree = treeify(data.split(' '))
console.log(tree)

// 8.1
const sum = sumMetas(tree)
console.log(sum)

// 8.2
const value = getRootValue(tree)
console.log(value)