Question

I have a fully built generic Trie in java. I am trying to traverse through the Trie to obtain all the complete combinations for each path. For example, if the Trie contained chars then it would return all the word combinations. For my purposes, I am trying to put all the nodes for each combination into an array and return them. I am stumped however. I only came up with the traversal that goes through each child (+ subchildren) before going back to the parent/starting node (much like a BST traversal). I am using an ArrayList to hold the children for each node. Sorry if it is a bit confusing. A code sample or pseudo code will be much appreciated. Thanks.

EDIT

By combinations, I mean the following. If I had a Trie<char> that looked like the following:

        "null"
       /  |   \
      a   i    t
     /   /|\    \
    t   f m n    o

The combinations that I would want returned would be:

[a, t]
[i, f]
[i, m]
[i, n]
[t, o]

and all these arrays/lists could be in one single ArrayList which is returned at the end.

Answer 1

Do a recursive method to (at least) get all the chars in the tree. Just make sure you initialize the chars as an empty List

Stack startRead(Tree tree) {
  // validation check
  if (tree == null || !tree.hasChild()) return null;

  // create Stack to store the lists
  Stack listStack = new Stack();

  // for every child
  List children = tree.getChildren();
  for (Tree child : children) {
    // create a list
    List childList = new ArrayList();

    // store (push) it into stack
    listStack.push(childList);

    // call the recursive
    readIt(child, listStack);
  }

  return listStack;
}

void readIt(Tree tree, Stack listStack) {
  // pick the top list from stack
  List current = (List) listStack.pop();

  // this is the base; if tree has no child don't call this method again.
  if (!tree.hasChild()) {
    // if it's leaf add the value to current list
    current.add(tree.getValue());

    // push it back to stack
    listStack.push(current);
  } else {
    // for every child
    List children = tree.getChildren();
    for (Tree child : children) {
      // IMPORTANT! clone the list (if this fails, clone it yourself)
      // clone is called when the tree is branching
      List childList = current.clone();

      // insert this tree value to list
      childList.add(tree.getValue());

      // push it back
      listStack.push(childList);

      // call again
      readIt(child, listStack);
    }
  }
}

with this you will have a return value of a Stack consisting Lists of value for each combination.

Hope this helps. 🙂