[LeetCode]103 Binary Tree Zigzag Level Order Traversal

https://oj.leetcode.com/problems/binary-tree-zigzag-level-order-traversal/

http://blog.csdn.net/linhuanmars/article/details/24509105

/**
 * 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) {
        
        if (root == null)
            return Collections. emptyList();
            
        List<List<Integer>> lists = new ArrayList<>();
    
        Queue<NodeWithLevel> queue = new LinkedList<>();
        queue.offer(new NodeWithLevel(root, 0));
        
        while (!queue.isEmpty())
        {
            NodeWithLevel levelnode = queue.poll();
            if (lists.size() == levelnode.level)
            {
                lists.add(new ArrayList<Integer>());
            }
            
            List<Integer> list = lists.get(levelnode.level);
            if (levelnode.level % 2 == 0)
                list.add(levelnode.node.val);
            else
                list.add(0, levelnode.node.val);
                
            if (levelnode.node.left != null)
                queue.offer(new NodeWithLevel(levelnode.node.left, levelnode.level + 1));
                
            if (levelnode.node.right != null)
                queue.offer(new NodeWithLevel(levelnode.node.right, levelnode.level + 1));
        }
        
        return lists;
    }
    
    private static class NodeWithLevel
    {
        private TreeNode node;
        private int level;
        NodeWithLevel(TreeNode node, int level)
        {
            this.node = node;
            this.level = level;
        }
    }
}