Print a Binary Tree Level by Level

printbylevel.java

// java.util.* and java.util.streams.* have been imported for this problem.
// You don't need any other imports.

public ArrayList<ArrayList<Integer>> printLevelByLevel(TreeNode root) {
                           
    
    ArrayList<Integer> nodeList = new ArrayList<Integer>();
    ArrayList<Integer> levelList = new ArrayList<Integer>();
    
     ArrayList<ArrayList<Integer>> myList = new ArrayList<ArrayList<Integer>>();

    if (root == null) {
        return myList;
    }
    
    Queue<TreeNode> currentQ = new LinkedList<TreeNode>();
    Queue<TreeNode> nextQ = new LinkedList<TreeNode>();
    
    currentQ.add(root);
    
    while(!currentQ.isEmpty()) {
        
        while(!currentQ.isEmpty()) {
            TreeNode node = currentQ.remove();
            if (node != null) {
                levelList.add(node.data);
                if(node.left!=null)
                    nextQ.add(node.left);
                if(node.right!=null)
                    nextQ.add(node.right);
            }
        }
        
        myList.add(levelList);
        levelList =new ArrayList<Integer>();
        
        while(!nextQ.isEmpty()) {
            currentQ.add(nextQ.remove());
        }
    }
    
    return myList;
}