get path to the children from parent

Question

I have a list of children and a list of parents. I also have a map of childeId-parentId. Parents can have n number of children but children have one immediate parent. I want to get the path to each child from parent in Java. How can I do it recursively?

I have groups as: [Root, abc, asd, xyz, 123, xyz2]

parent-child map: {Root=abc, Root=asd, Root=xyz, Root=123, xyz=xyz2}

I want to get path of each child as: {Root/abc, Root/asd, Root/xyz, Root/123, Root/xyz/xyz2}

I have a map :

final<String, Groups> groupMap = Service.getListOfGroups(service);

which gives me all the required values. I am looping through the map to get each entry.

public Map<String, Groups> takeGroups(Service servie ) {
final<String, Groups> groupMap = new HashMap<>();
for(Groups gp: service.getGroups()){
groupMap.put(gp.getGroupId, gp)
}
for(Groups gp: groupMap.values()){
   gp.setChildren(new ArrayList<>());
   String group = gp.getGroupValue();
   String parentId = gp.getParent();
   Groups parentGroup = groupMap.get(parentId);
   List<GroupSummary> childs = parent.getChildren();
   if(childs == null){
      childs = new ArrayList<>();
   }
   childs.add(gd);
 } 
 return groupMap;
}

I think I can solve this by adding all these values to n-ary tree and then traversing through n-ary tree. I have never worked with trees before and not sure how can I create n-ary-tree from this and get the required paths to all the groups. Really appreciate any help.

Answer 1

Something like this should do it. Note that I have not tried to compile it, so it almost certainly has syntax errors. But it should serve to give you an idea of what you have to do.

public List<Node> getPath( Node node, Map<Node,Node> childToParentMap )
{
    List<Node> path = new ArrayList<>();
    return fillPath( node, path );
}

private void fillPath( Node node, Map<Node,Node> childToParentMap, List<Node> path )
{
    Node parent = childToParentMap.get( node );
    if( parent != null )
        fillPath( parent, childToParentMap, path );
    path.add( node );
}