challenge.js

function canIMake(list, target) {
  if (target === 1) return true
  if (target === 0) return false
  if (list.length === 0) return false
  if (list.length === 1) {
    if (list[0] % target !== 0) return false
    return true
  }

  const modded = list.map(val => val % target)
  return calculate(modded, 1, target, [modded[0], -modded[0]])
}

function calculate(list, position, target, runningTotals) {
  if (position == list.length) {
    const midpoint = Math.ceil(runningTotals.length / 2)
    return runningTotals.slice(0, midpoint).indexOf(0) !== -1
  }

  const newTotals = []
  for (let i = 0; i < runningTotals.length; i++) {
    const curr = runningTotals[i]
    newTotals.push(curr + list[position], curr - list[position])
  }

  return calculate(list, position + 1, target, newTotals)
}

canIMake([1,2,3,4,6], 4) // true
canIMake([1,3,9], 2) // false