Binary Tree Zigzag Level Order Traversal

public class Solution {
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        List<List<Integer>> rst = new ArrayList<List<Integer>>();
        if(root == null)    return rst;
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        int count = 1;
        while(!queue.isEmpty())
        {
            int size = queue.size();
            List<Integer> list = new ArrayList<Integer>();
            for(int i = 0; i < size; i++)
            {
                TreeNode node = queue.poll();
                if(node.left != null)   queue.offer(node.left);
                if(node.right != null)  queue.offer(node.right);
                list.add(node.val);
            }
            if(count%2 == 1)
            {
                rst.add(list);
            }
            else
            {
                Collections.reverse(list);
                rst.add(list);
            }
            count++;
        }
        return rst;
    }
}

public class Solution {
    public ArrayList<ArrayList<Integer>> zigzagLevelOrder(TreeNode root) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();

        if (root == null) {
            return result;
        }

        Stack<TreeNode> currLevel = new Stack<TreeNode>();
        Stack<TreeNode> nextLevel = new Stack<TreeNode>();
        Stack<TreeNode> tmp;
        
        currLevel.push(root);
        boolean normalOrder = true;

        while (!currLevel.isEmpty()) {
            ArrayList<Integer> currLevelResult = new ArrayList<Integer>();

            while (!currLevel.isEmpty()) {
                TreeNode node = currLevel.pop();
                currLevelResult.add(node.val);

                if (normalOrder) {
                    if (node.left != null) {
                        nextLevel.push(node.left);
                    }
                    if (node.right != null) {
                        nextLevel.push(node.right);
                    }
                } else {
                    if (node.right != null) {
                        nextLevel.push(node.right);
                    }
                    if (node.left != null) {
                        nextLevel.push(node.left);
                    }
                }
            }

            result.add(currLevelResult);
            tmp = currLevel;
            currLevel = nextLevel;
            nextLevel = tmp;
            normalOrder = !normalOrder;
        }

        return result;

    }
}