Binary Tree Zigzag Level Order Traversal

Java

class Solution {
		public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
		
		List<List<Integer>> result = new ArrayList<>();
		if (root == null) return result;
		
				Queue<TreeNode> queue = new LinkedList<>();
				
				Boolean flag = true;
				queue.offer(root);
				while (!queue.isEmpty()) {
					List<Integer> path = new ArrayList<>();
					int size = queue.size();
					for (int i = 0; i < size; i++) {
						TreeNode temp = queue.poll();
						path.add(temp.val);
						if (temp.left != null) queue.offer(temp.left);
						if (temp.right != null) queue.offer(temp.right);
					}
					
					if (!flag) Collections.reverse(path);
					result.add(new ArrayList<>(path));
		flag = !flag;
				}
				return result;
		}
}