Complete the below function wh | CareerCup


Complete the below function wh | CareerCup

Complete the below function which takes an arraylist and displays the list in the expected output

public class TreePrinter {
public static void printTree(Iterable<Relation> rs) {
// your code

}
}

public static class Relation {
String parent;
String child;
public Relation(String parent, String child) { ... }
}
}

Example input:
List<Relation> input = newArrayList();

input.add(new Relation("animal", "mammal"));
input.add(new Relation("animal", "bird"));
input.add(new Relation("lifeform", "animal"));
input.add(new Relation("cat", "lion"));
input.add(new Relation("mammal", "cat"));
input.add(new Relation("animal", "fish"));

TreePrinter.printTree(input);

Expected output:
line 1: lifeform
line 2: animal
line 3: mammal
line 4: cat
line 5: lion
line 6: bird
line 7: fish

 public void printTree(Iterable<Relation> rs){
  
  //build a tree like below with lifeform as root 
  //and do a traversal.
  //lifeform -- animal
  //animal -- mammal -- cat-- lion
  //animal -- bird
  //animal -- fish
  
  //use this set to keep track of children to find out 
  //which one is the root node.
  Set<String> setOfNotRootElements = new HashSet<String>();
  
  //build a tree using HashMap. You can also build the tree 
  //put a Map inside a Map, but this seems simpler.
  HashMap<String, List<String>> map = new HashMap<String, List<String>>();
  for(Relation r: rs){
   List<String> children =  new ArrayList<String>();
   if(map.containsKey(r.parent)){
    children = map.get(r.parent);
   }
   children.add(r.child);
   map.put(r.parent, children );
   
   //keeping track of children..
   setOfNotRootElements.add(r.child);
  }
  
  //find the root
  Set<String> diffSet = new HashSet<String>(map.keySet());
  diffSet.removeAll(setOfNotRootElements);
  String root = diffSet.iterator().next();
  
  //traverse the tree.
  printNode(root, map);
  
  //lifeform
  //animal
  //mammal
  //cat
  //lion
  //bird
  //fish
 }
 
 public void printNode(String parent, HashMap<String, List<String>> map){
  System.out.println(parent);
  List<String> children = map.get(parent);
  if(children != null){
   for(String child: children){
    printNode(child, map);
   }
  }
 }

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