containsExactHalvesSubarray.js

function containsExactHalvesSubarray(v) {
  const hash = {}
  v = v.sort((a,b) => parseInt(a)-parseInt(b));

  v.forEach(i => {
    if (i < 0)
      if (hash[i]) hash[i][0] = true
      else hash[i/2] = [null,true]
    else
      if (hash[i/2]) hash[i/2][1] = true
      else hash[i] = [true,null]
  })

  return Object.keys(hash).every(key => hash[key][0] == hash[key][1])
}