Java indentation in Level-order Tree print, not binary tree

Question

I want to print my non-binary tree with level-order traverse. In the code below I indent every time a new set of children has been added, but somehow I need to remove indentations when I go back in the tree again. Here's how this tree prints:

Root
  Home
    HomeChild1
    HomeChild2
    Documents (should be same level as Home)
      DocumentChild1
      DocumentChild2
      Downloads (should be same level as Home and Documents)
        DownloadsChild1

Code:

queue.add(o);  //root
        int indent = 0;
        while(!queue.isEmpty(){

            for(int i=0; i<indent; i++){
                print("  ");
            }

            Object tempObj = queue.remove(o);
            print(tempObj.value);

            if(tempObj.children != null){
                //Adding all childrens, since its not a binary tree I loop throught all children
                for(int i=0; i<tempObj.children.length; i++){
                    queue.add(0, tempObj.children[i];
                }
                indent++;
            }
        }

Here is what I want it to look like

Root
  Home
    HomeChild1
    HomeChild2
  Documents
    DocumentChild1
    DocumentChild2
  Downloads
    DownloadsChild1

score 2 · Accepted Answer · answered May 03 '17 at 12:59

2

You need to increment the indent when you start processing children, and then decrement it when you reach the end of a group of children.

You would be better off doing this whole thing using something like a recursive call rather than the queue though. The queue is adding a lot of complexity and not helping.

Something like:

recurseTree(Thing obj, String indent) {
    print(indent+obj.value);
    if (obj.children != null) {
       for (Thing child: obj.children) {
          recurseTree(child, indent+"   ");
       }
    }
}

You could make some optimisations here (for example only doing the string concatonation once) and you will need to do a bit of tidying up but that should give you the basic framework you need.

Start it using

recurseTree(root, "");

answered May 03 '17 at 12:59

Tim B

40,716
16
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Thanks! Works good now, weird I didnt find a recursive solution when I searched for Java Breadth-first algorithm xD – Simon Andersson May 03 '17 at 13:27
@SimonAndersson This is one of the classic use-cases for recursion so I'm surprised nothing came up. – Tim B May 03 '17 at 13:29
Yes but the Depths-first is much more common, maybe thats why – Simon Andersson May 03 '17 at 13:31
Well this is depth first really, but that's what you said you wanted in your description of the output. – Tim B May 03 '17 at 13:33
Oh thats true, guess my head isnt up too speed right now ;) thanks again – Simon Andersson May 03 '17 at 13:38

rilent · Answer 2 · 2017-05-03T13:01:03.317

0

You never reset your indent value. You need to copy its value so you can restore it after you went through a group of children

Btw, if you try something recursive it's way easier to handle.

edited May 03 '17 at 13:01

answered May 03 '17 at 12:54

rilent

659
1
6
22

First while loop, it adds all level 1 children to the queue, (home, documents,downloads). and next loop it removes home and add all homes children first in the queue, Im not sure where I need to reset the indent value – Simon Andersson May 03 '17 at 12:57
Tim B algorithm is simply the best to do what you are trying to achieve. – rilent May 03 '17 at 13:02

Java indentation in Level-order Tree print, not binary tree

2 Answers2