Print the nodes of binary tree column-wise, using recursion and iteration

Question

I am trying to code for both recursive and iterative approach to a problem.

Below is a recursive code to print the nodes of binarytree column wise. Basically I have count of root as 0 and if I move left I decrement count by 1 and if I move right I increment the count by 1:

public void printcolumnOrder_recursive(Tree curr,int count){ if(curr == null) return; if(hm.get(count)!=null){ List l = hm.get(count); l.add(curr.data); hm.put(count, l); } else{ List l = new ArrayList<Integer>(); l.add(curr.data); hm.put(count,l); } printcolumnOrder_recursive(curr.left,count-1); printcolumnOrder_recursive(curr.right,count+1); } 

I converted it to an iterative approach:

 Stack<Tree> st = new Stack<Tree>(); Stack<Integer> ct = new Stack<Integer>(); Tree node = curr; st.push(node); ct.push(0); while(!st.isEmpty()){ Tree temp=st.pop(); int count = ct.pop(); if(hm.get(count)!=null){ List l = hm.get(count); l.add(temp.data); hm.put(count, l); } else{ List l = new ArrayList<Integer>(); l.add(temp.data); hm.put(count,l); } if(temp.right!=null){ st.push(temp.right); ct.push(count+1); } if(temp.left!=null){ st.push(temp.left); ct.push(count-1); } } for(Integer key: hm.keySet()){ for(Integer i: hm.get(key)){ System.out.print(" " + i); } System.out.println(""); } 

Both implementations work fine.

I have used 2 stacks in the iterative approach, one for nodes in a tree and the other for count.

Do we need a stack for count? Is there a better way to do it?