Building hierarchy objects from flat list of parent/child

Question

I have a list of items in a hierarchy, and I\'m attempting to parse this list out into an actual hierarchy of objects. I\'m using modified pre-order tree traversal to store/iter

Answer 1

Alternative version that compiles normally, I wasn't sure if there was a problem with the code above.

private List FlatToHierarchy(List list) {
      // hashtable lookup that allows us to grab references to the parent containers, based on id
        Dictionary lookup = new Dictionary();
      // actual nested collection to return
      List nested = new List();

      foreach(Page item in list) {
        if (lookup.ContainsKey(item.parentId)) {
          // add to the parent's child list 
          lookup[item.parentId].children.Add(item); //add item to parent's childs list
          lookup.Add(item.pageId, item); //add reference to page in lookup table
        } else {
          // no parent added yet (or this is the first time)
          nested.Add(item);     //add item directly to nested list                
          lookup.Add(item.pageId, item); //add reference to page in lookup table
        }
      }
    return nested;
    }