/*
 * @lc app=leetcode id=103 lang=java
 *
 * [103] Binary Tree Zigzag Level Order Traversal
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        if(root == null) {
            return new ArrayList<>();
        }
        boolean reverse = false;
        List<List<Integer>> ret = new ArrayList<>();
        LinkedList<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        TreeNode layerEndNode = null, curNode = null;
        List<Integer> cache = new ArrayList<>();
        while(!queue.isEmpty()) {
            TreeNode tmp = queue.pollFirst();
            cache.addLast(tmp.val);
            if(tmp.left != null) {
                queue.addLast(tmp.left);
                curNode = tmp.left;
            }
            if(tmp.right != null) {
                queue.addLast(tmp.right);
                curNode = tmp.right;
            }
            if(layerEndNode == null || layerEndNode == tmp) {
                layerEndNode = curNode;
                if(reverse) {
                    ret.add(cache.reversed());
                } else {
                    ret.add(cache);
                }
                cache = new ArrayList<>();
                reverse = !reverse;
            }
        }
        return ret;
    }
}
// @lc code=end