Identify all Grand-Parent Nodes of each Node in a Map

Given in input that has relationships between a person and their children, for all the people in this data, identify grandparents of all the people in the input.

Input: A map of all the people and their children
Map[String, Set[String]]

Output: A map of all people and their grandparents
Map[String, Set[String]]

Example:
Input 
Map(A -> Set(B,C), B -> Set(D, C), C -> Set(E))

Output:
Map(D -> Set(A), C -> Set(A), E -> Set(A, B)) 

We strongly recommend you to minimize your browser and try this yourself first

Here we have iterate over each and every node in Map and find out the grand-parent of each child.

The idea is to use Recursion. But, it can be solved without Recursion too.

Lets see the Without Recursion solution first:

Solution 1 (Without Recursion):

Here we have to use Mutable Scala Map. Below is the Scala Code.

val input = Map("A" -> Set("B","C"), "B" -> Set("D", "C"), "C" -> Set("E"))
val output: scala.collection.mutable.Map[String, Set[String]]
  = scala.collection.mutable.Map()

  input.map(node => node._2.map(child =>
    input.get(child).map(grandchildren =>
      grandchildren.map{grandchild =>
        if(output.keys.exists(_ == grandchild)) {
          output.put(grandchild, output.get(grandchild).get ++ Set(node._1))
        } else {
          output.put(grandchild, Set(node._1))
        }
      }
    )
  ))

Here we are iterating over every Node of Map and finding out the grandchildren of each child in node.This, will help us in creating a Map with Grand-Child and Grand-Parents relationship.

Solution 2 (With Recursion):

Here we can use Immutable Scala Map as we are using Recursion.

val input = Map("A" -> Set("B","C"), "B" -> Set("D", "C"), "C" -> Set("E"))
val output = findGrandparents(input)

  def findGrandparents(family: Map[String, Set[String]]): Map[String, Set[String]] = {
    family.foldLeft(Map[String, Set[String]]()){
      case (grandParents, oneFamily) => {
        val grandChildren: Set[String] = oneFamily._2.flatMap(member => family.get(member)).flatten
        val res =  grandChildren.map(child => {
          grandParents.get(child) match {
            case None =>(child -> Set(oneFamily._1))
            case Some(x) => (child -> (x + oneFamily._1))
          }
        }).toMap
        grandParents ++ res
      }

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