public List <string> Run(List <CourseEntry> input)
{
var orphans = new Dictionary <int, List <CourseNode> >();
var seenNodes = new Dictionary <int, CourseNode>();
var roots = new Dictionary <int, CourseNode>();
var toReturn = new List <string>();
foreach (var course in input)
{
var parent = course.ParentID;
var courseNode = new CourseNode(course.ID, course.Name);
seenNodes.Add(courseNode.ID, courseNode);
// if the node is a root
if (parent == -1)
{
roots.Add(courseNode.ID, courseNode);
}
// the node is not a root, find its parent
// first, check if we have seen its parent
if (seenNodes.ContainsKey(parent))
{
// add the node to this parent
seenNodes[parent].Children.Add(courseNode);
}
else
{
// it is an orphan, add it to the orphan list
if (!orphans.ContainsKey(parent))
{
orphans.Add(parent, new List <CourseNode>());
}
orphans[parent].Add(courseNode);
}
// now this node need to collect the orphans
if (orphans.ContainsKey(courseNode.ID))
{
var children = orphans[courseNode.ID];
foreach (var child in children)
{
courseNode.Children.Add(child);
}
orphans.Remove(courseNode.ID);
}
}
foreach (var root in roots.Values)
{
PrintChildren(root, "", toReturn);
}
return(toReturn);
}
public void PrintChildren(CourseNode node, string prefix, List <string> toReturn)
{
toReturn.Add($"{prefix}{node.Name}");
if (node.Children.Count > 0)
{
foreach (var child in node.Children)
{
PrintChildren(child, prefix + "-", toReturn);
}
}
}