Binary Tree Level Order Zig-Zag Traversal

BinaryTreeLevelOrderZigZag.java

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        LinkedList<Integer> list= new LinkedList<Integer>();
        List<List<Integer>> listList= new ArrayList<List<Integer>>();
        
        if (root == null) return listList;
        
        Queue<TreeNode> treeQueue = new LinkedList<TreeNode>();
        
        int countCurrentLevel = 1;
        int countNextLevel = 0;
        boolean goLeft = false;
        
        treeQueue.add(root);
        while (!treeQueue.isEmpty()){
            TreeNode node = treeQueue.remove();
           
            countCurrentLevel--;
            if (goLeft){
                list.addFirst(node.val);
                if (node.left != null){
                    treeQueue.add(node.left);
                    countNextLevel++;
                }
                if (node.right != null){
                    treeQueue.add(node.right);
                    countNextLevel++;
                }
            }
            else{
                list.add(node.val);
                if (node.left != null){
                    treeQueue.add(node.left);
                    countNextLevel++;
                }
                if (node.right != null){
                    treeQueue.add(node.right);
                    countNextLevel++;
                }
                
                
            }
            
            if (countCurrentLevel == 0){
                goLeft = (goLeft == true? false : true);
                listList.add(list);
                list = new LinkedList<Integer>();
                countCurrentLevel = countNextLevel;
                countNextLevel = 0;
            }
            
        }
        return listList;
        
    }
}