二叉树锯齿形遍历

 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class  {
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {       
        List<List<Integer>> wrapList=new LinkedList<List<Integer>>();
        if(root==null)
            return wrapList;
        boolean flag=true;
        Queue<TreeNode> queue=new LinkedList<TreeNode>();
        queue.offer(root);
      
        while(!queue.isEmpty())
        {         
              int level=queue.size();
            List<Integer> subList=new LinkedList<>();
             
       
             
            for(int i=0;i<level;i++)
            {
                 TreeNode n=queue.poll();
                    if(flag)
            {
                subList.add(n.val);
            }
            else
            {
                subList.add(0,n.val);
            }
                        if(n.left!=null)
                        queue.offer(n.left);
                         if(n.right!=null)
                        queue.offer(n.right);
                }
            flag=flag?false:true;
            wrapList.add(subList);
        }
          return wrapList;
        }     
    }