NumberOfParents.js

function findZeroOrOneParentage(input)
{
  var objects = {}
  var set = new Set()

  input.forEach(function(elem){
    if(objects[elem[0]] === undefined)
      objects[elem[0]] = []  
    if(objects[elem[1]] === undefined)
      objects[elem[1]] = []

    objects[elem[0]].push(elem[1])
    set.add(elem[0]).add(elem[1])
  })

  var result = [[],[]]
  set.forEach(function(value) {
    if(objects[value].length === 0)
      result[0].push(value)
    else if(objects[value].length === 1)
      result[0].push(value)
  })

  return result
}