题目：
题解：
class Solution {public List<List<Integer>> zigzagLevelOrder(TreeNode root) {List<List<Integer>> ans = new LinkedList<List<Integer>>();if (root == null) {return ans;}Queue<TreeNode> nodeQueue = new ArrayDeque<TreeNode>();nodeQueue.offer(root);boolean isOrderLeft = true;while (!nodeQueue.isEmpty()) {Deque<Integer> levelList = new LinkedList<Integer>();int size = nodeQueue.size();for (int i = 0; i < size; ++i) {TreeNode curNode = nodeQueue.poll();if (isOrderLeft) {levelList.offerLast(curNode.val);} else {levelList.offerFirst(curNode.val);}if (curNode.left != null) {nodeQueue.offer(curNode.left);}if (curNode.right != null) {nodeQueue.offer(curNode.right);}}ans.add(new LinkedList<Integer>(levelList));isOrderLeft = !isOrderLeft;}return ans;}
}